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 Silver Princess brass Gramps tank car in original box
HOn3 Silver Princess brass Gramps tank car in original box
$65.00
Time Remaining: 1d 20h 32m
Buy It Now for only: $65.00
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
$33.99
Time Remaining: 4d 8h 32m
Buy It Now for only: $33.99
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: 6d 14h 23m
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: 6d 14h 26m
Buy It Now for only: $45.16
ON30 AMS Tank Car Shell SCCX A 09
ON30 AMS Tank Car Shell SCCX A 09
$45.00
Time Remaining: 18d 19h 4m
Buy It Now for only: $45.00
ON30 AMS Tank Car Standard Oil 106
ON30 AMS Tank Car Standard Oil 106
$45.00
Time Remaining: 20d 22h 12m
Buy It Now for only: $45.00
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: 22d 16h 37m
Buy It Now for only: $89.95
Spectrum Bachmann 27146 ON30 Freight TANK CAR ZEROLENE NEW in Box
Spectrum Bachmann 27146 ON30 Freight TANK CAR ZEROLENE NEW in Box
$49.95
Time Remaining: 23d 10h 10m
Buy It Now for only: $49.95
Spectrum Bachmann 27199 ON30 Freight TANK CAR BLACK UNLETTERED NEW in Box
Spectrum Bachmann 27199 ON30 Freight TANK CAR BLACK UNLETTERED NEW in Box
$49.95
Time Remaining: 23d 10h 14m
Buy It Now for only: $49.95
Bachmann Spectrum  27145 On30 Freight CAR  TANK CAR GRAMPS 
Bachmann Spectrum  27145 On30 Freight CAR  TANK CAR GRAMPS 
$40.00
Time Remaining: 23d 15h 58m
Buy It Now for only: $40.00
bachmann hawthorne village BUDWEISER tank car On3O scale
bachmann hawthorne village BUDWEISER tank car On3O scale
$32.75
Time Remaining: 29d 15h 9m
Buy It Now for only: $32.75

Other On30 Scale train items recently purchased through this site:

bachmann hawthorne village BUDWEISER tank car On3O scale
ON30 AMS Tank Car Shell SCCX A 09
On3 On30 WISEMAN MODEL SERVICES WEST SIDE LUMBER CO OIL TANK CAR 5 KIT
ON30 AMS Tank Car Standard Oil 106
Lot of 2 BLACKSTONE HOn3 B370110 DRGW UTLX 48 Bettendorf Tank Car Trucks
Spectrum Bachmann 27199 ON30 Freight TANK CAR BLACK UNLETTERED NEW in Box
HOn3 Silver Princess brass Gramps tank car in original box
Spectrum Bachmann 27146 ON30 Freight TANK CAR ZEROLENE NEW in Box
Bachmann Spectrum  27145 On30 Freight CAR  TANK CAR GRAMPS 
Bachmann On30 Scale Train Tank Car Tank Car Standard Oil 27131
Bachmann On30 Scale Train Tank Car Tank Car DS Fire Suppression 27122