I'm guessing that these troop cars have Allied Full Cushion trucks, common on these cars but otherwise rather rare among most rolling stock.
As such, your best bet would be to contact Atlas, the current producer of the Weaver troop cars, and see if they are available for separate sale. Although Atlas has re-issued the troop cars and have the correct Allied Full Cushion trucks, I don't find the trucks listed for separate sale on their website...O-scale/trucks. And, that's too bad, because I'd love to have a couple pairs of the AFC trucks...some roads (e.g., RI, ATSF, et al) re-equipped boxcars with these trucks for express service...passenger/mail trains, typically. In O scale it's not a commonly available truck...plastic or metal. In fact, although Weaver listed these for separate sale when they were in business, they were available only for a short time...then no more.
FWIW...
KD