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

HOn3 BLACKSTONE GRAMPS FRAMELESS TANK CAR 55276
HOn3 BLACKSTONE GRAMPS FRAMELESS TANK CAR 55276
$65.00
Time Remaining: 3d 8h 38m
Buy It Now for only: $85.00
San Juan Car Co Gramps Tank Car Set 63 88131
San Juan Car Co Gramps Tank Car Set 63 88131
$600.00
Time Remaining: 3d 11h 53m
Buy It Now for only: $600.00
San Juan Car Co Gramps Tank Car Set 88153 88166
San Juan Car Co Gramps Tank Car Set 88153 88166
$500.00
Time Remaining: 3d 12h 6m
Buy It Now for only: $500.00
Westside type Detailed Hon3 BRASS SINGLE DOME TANK CAR OB VG+Deal
Westside type Detailed Hon3 BRASS SINGLE DOME TANK CAR OB VG+Deal
$54.99
Time Remaining: 4d 17h 20m
Buy It Now for only: $54.99
On3 On30 WISEMAN MODEL SERVICES WEST SIDE LUMBER CO OIL TANK CAR 5 KIT
On3 On30 WISEMAN MODEL SERVICES WEST SIDE LUMBER CO OIL TANK CAR 5 KIT
$89.95
Time Remaining: 18d 13h 24m
Buy It Now for only: $89.95
HOn3 Silver Princess brass Gramps tank car in original box
HOn3 Silver Princess brass Gramps tank car in original box
$65.00
Time Remaining: 27d 17h 18m
Buy It Now for only: $65.00
Iron Horse Brass HOn3 GRAMPS Frameless Tank Car UNUSED
Iron Horse Brass HOn3 GRAMPS Frameless Tank Car UNUSED
$179.99
Time Remaining: 30d 1h 59m
Buy It Now for only: $179.99
Lot of 2 BLACKSTONE HOn3 B370110 DRGW UTLX 48 Bettendorf Tank Car Trucks
Lot of 2 BLACKSTONE HOn3 B370110 DRGW UTLX 48 Bettendorf Tank Car Trucks
$34.99
Time Remaining: 30d 5h 19m
Buy It Now for only: $34.99
Bachmann On30 Scale Train Tank Car Tank Car DS Fire Suppression 27122
Bachmann On30 Scale Train Tank Car Tank Car DS Fire Suppression 27122
$45.16
Time Remaining: 32d 11h 10m
Buy It Now for only: $45.16
Bachmann On30 Scale Train Tank Car Tank Car Standard Oil 27131
Bachmann On30 Scale Train Tank Car Tank Car Standard Oil 27131
$45.16
Time Remaining: 32d 11h 12m
Buy It Now for only: $45.16

Other On30 Scale train items recently purchased through this site:

San Juan Car Co Gramps Tank Car Set 63 88131
San Juan Car Co Gramps Tank Car Set 88153 88166
HOn3 BLACKSTONE GRAMPS FRAMELESS TANK CAR 55276
Westside type Detailed Hon3 BRASS SINGLE DOME TANK CAR OB VG+Deal
Bachmann On30 Scale Train Tank Car Tank Car Standard Oil 27131
On3 On30 WISEMAN MODEL SERVICES WEST SIDE LUMBER CO OIL TANK CAR 5 KIT
Lot of 2 BLACKSTONE HOn3 B370110 DRGW UTLX 48 Bettendorf Tank Car Trucks
HOn3 Silver Princess brass Gramps tank car in original box
Bachmann On30 Scale Train Tank Car Tank Car DS Fire Suppression 27122
Iron Horse Brass HOn3 GRAMPS Frameless Tank Car UNUSED