We've searched the internet and found the largest collection of On30 Scale trains for sale is on eBay. Below are the listings for 'boxcar'.

BINKLEY KIT BUILT HOn3 NARROW GAUGE DENVER RIO GRANDE DRGW BOX CAR WAGON 315 nd
BINKLEY KIT BUILT HOn3 NARROW GAUGE DENVER RIO GRANDE DRGW BOX CAR WAGON 315 nd
$68.98
Time Remaining: 2d 8h 48m
Buy It Now for only: $68.98
ON3 ON30 SILVER CITY MODELS DRGW 1872 12 4 WHEEL BOX CAR KIT
ON3 ON30 SILVER CITY MODELS DRGW 1872 12 4 WHEEL BOX CAR KIT
$36.00
Time Remaining: 5d 21h 20m
Buy It Now for only: $36.00
HAWTHORNE VILLAGE On30 BACHMANN CONFEDERATE CIVIL WAR J E B STUART BOX CAR 005
HAWTHORNE VILLAGE On30 BACHMANN CONFEDERATE CIVIL WAR J E B STUART BOX CAR 005
$59.99
Time Remaining: 10d 22h 24m
Buy It Now for only: $59.99
Hawthorne Village The Northern Lights Box Car with track
Hawthorne Village The Northern Lights Box Car with track
$80.00
Time Remaining: 10d 23h 19m
Buy It Now for only: $80.00
BINKLEY KIT BUILT HOn3 NARROW GAUGE DSPPRR DENVER SOUTH PARK REEFER BOX CAR 605
BINKLEY KIT BUILT HOn3 NARROW GAUGE DSPPRR DENVER SOUTH PARK REEFER BOX CAR 605
$68.98
Time Remaining: 11d 17h 8m
Buy It Now for only: $68.98
HAWTHORNE VILLAGE On30 BACHMANN CONFEDERATE CIVIL WAR STONEWALL J BOX CAR 006
HAWTHORNE VILLAGE On30 BACHMANN CONFEDERATE CIVIL WAR STONEWALL J BOX CAR 006
$59.99
Time Remaining: 12d 17h 42m
Buy It Now for only: $59.99
HAWTHORNE VILLAGE On30 BACHMANN CONFEDERATE CIVIL WAR NORTHERN LIGHTS BOX CAR 02
HAWTHORNE VILLAGE On30 BACHMANN CONFEDERATE CIVIL WAR NORTHERN LIGHTS BOX CAR 02
$59.99
Time Remaining: 13d 11h 18m
Buy It Now for only: $59.99
BINKLEY KIT BUILT HOn3 NARROW GAUGE DENVER RIO GRANDE DRGW BOX CAR WAGON 3145 n
BINKLEY KIT BUILT HOn3 NARROW GAUGE DENVER RIO GRANDE DRGW BOX CAR WAGON 3145 n
$68.98
Time Remaining: 14d 5h 6m
Buy It Now for only: $68.98
HAWTHORNE VILLAGE BACHMANN CONFEDERATE CIVIL WAR NORTHERN LIGHTS BOX CAR 02
HAWTHORNE VILLAGE BACHMANN CONFEDERATE CIVIL WAR NORTHERN LIGHTS BOX CAR 02
$34.00
Time Remaining: 14d 12h 22m
Buy It Now for only: $34.00
BINKLEY KIT BUILT HOn3 NARROW GAUGE DSPPRR DENVER SOUTH PARK REEFER BOX CAR 606
BINKLEY KIT BUILT HOn3 NARROW GAUGE DSPPRR DENVER SOUTH PARK REEFER BOX CAR 606
$68.98
Time Remaining: 19d 9h 9m
Buy It Now for only: $68.98
Hawthorne Village Civil War  The Northern Lights  Boxcar NOS C 9 2003 On30
Hawthorne Village Civil War The Northern Lights Boxcar NOS C 9 2003 On30
$29.99
Time Remaining: 20d 16h 43m
Buy It Now for only: $29.99
Hawthorne Village Civil War  The Night Conference Box Car  NOS C 9 2003
Hawthorne Village Civil War The Night Conference Box Car NOS C 9 2003
$29.99
Time Remaining: 20d 18h 10m
Buy It Now for only: $29.99
BINKLEY KIT BUILT HOn3 NARROW GAUGE DSPPRR DENVER SOUTH PARK REEFER BOX CAR 603
BINKLEY KIT BUILT HOn3 NARROW GAUGE DSPPRR DENVER SOUTH PARK REEFER BOX CAR 603
$68.98
Time Remaining: 22d 14h 55m
Buy It Now for only: $68.98
Bachmann On30 18BOXCARS Undec 2pcs BAC26501
Bachmann On30 18BOXCARS Undec 2pcs BAC26501
$83.30
Time Remaining: 26d 11h 29m
Buy It Now for only: $83.30
BINKLEY KIT BUILT HOn3 NARROW GAUGE DENVER RIO GRANDE DRGW BOX CAR WAGON 15 nd
BINKLEY KIT BUILT HOn3 NARROW GAUGE DENVER RIO GRANDE DRGW BOX CAR WAGON 15 nd
$68.98
Time Remaining: 27d 6h 50m
Buy It Now for only: $68.98
HOn3 CUSTOM BUILT 24 TRUS ROD WOOD BOXCAR KDs STEEL WHEELS PAINTEDb
HOn3 CUSTOM BUILT 24 TRUS ROD WOOD BOXCAR KDs STEEL WHEELS PAINTEDb
$29.95
Time Remaining: 28d 22h 23m
Buy It Now for only: $29.95
HOn3 CUSTOM BUILT 24 TRUS ROD WOOD BOXCAR KDs STEEL WHEELS PAINTEDa
HOn3 CUSTOM BUILT 24 TRUS ROD WOOD BOXCAR KDs STEEL WHEELS PAINTEDa
$29.95
Time Remaining: 28d 22h 24m
Buy It Now for only: $29.95
HOn3 CUSTOM BUILT 24 TRUS ROD WOOD BOXCAR KDs STEEL WHEELS PAINTEDc
HOn3 CUSTOM BUILT 24 TRUS ROD WOOD BOXCAR KDs STEEL WHEELS PAINTEDc
$29.95
Time Remaining: 28d 22h 24m
Buy It Now for only: $29.95
On30 Fat Albert Boxcar Conversion to fit Bachmann 18ft flat car
On30 Fat Albert Boxcar Conversion to fit Bachmann 18ft flat car
$37.00
Time Remaining: 29d 16h 25m
Buy It Now for only: $37.00

Other On30 Scale train items recently purchased through this site:

HOn3 CUSTOM BUILT 24 TRUS ROD WOOD BOXCAR KDs STEEL WHEELS PAINTEDc
HOn3 CUSTOM BUILT 24 TRUS ROD WOOD BOXCAR KDs STEEL WHEELS PAINTEDb
HOn3 CUSTOM BUILT 24 TRUS ROD WOOD BOXCAR KDs STEEL WHEELS PAINTEDa
On30 Fat Albert Boxcar Conversion to fit Bachmann 18ft flat car
ON3 ON30 SILVER CITY MODELS DRGW 1872 12 4 WHEEL BOX CAR KIT
Hawthorne Village The Northern Lights Box Car with track
Hawthorne Village Civil War The Night Conference Box Car NOS C 9 2003
Hawthorne Village Civil War The Northern Lights Boxcar NOS C 9 2003 On30
HAWTHORNE VILLAGE BACHMANN CONFEDERATE CIVIL WAR NORTHERN LIGHTS BOX CAR 02
HAWTHORNE VILLAGE On30 BACHMANN CONFEDERATE CIVIL WAR STONEWALL J BOX CAR 006
Bachmann On30 18BOXCARS Undec 2pcs BAC26501
HAWTHORNE VILLAGE On30 BACHMANN CONFEDERATE CIVIL WAR NORTHERN LIGHTS BOX CAR 02
HAWTHORNE VILLAGE On30 BACHMANN CONFEDERATE CIVIL WAR J E B STUART BOX CAR 005