For that, you might be better off seeing if you can find lineart of the images you want (for example, from scans of the instruction bookets for either Predaking or the individual Predacons, or G1 S3 DVD screencaps), converting the section you want to vector art, adding colour fills and then scaling it to the dimensions you want for the T-shirt.

That should work for toy-based flat-colour art, anyway. If you want a more 3D look, track down high-resolution photos of the toys (seibertron.com, maybe?) and use those, or perhaps someone here might oblige with their own Predaking.

Of course, if you're after something that looks like it should be airbrushed onto the side of a van and wouldn't be out of place with barbarian amazons in chrome bikinis, you might have to get them customised...