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'.

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: 25d 21h 37m
Buy It Now for only: $89.95

Other On30 Scale train items recently purchased through this site:

On3 On30 WISEMAN MODEL SERVICES WEST SIDE LUMBER CO OIL TANK CAR 5 KIT