In my opinion the best option is to just make your own stuff. Most of the tee shirt designs I see available aren't really what I'm interested in so most of my DMC related clothing is stuff I've designed myself. The copyright for the DMC logo (non embossed looking one) like you see on the front of the car has expired and is fair use. Plus if you're just making things for yourself and not selling it you're not going to get sued anyway.
Free vector file here:
https://www.brandsoftheworld.com/log...-motor-company
My brother works for a graphic design shop and he makes me all kinds of stuff... embroidered hats, screen printed shirts, iron on transfers onto stuff, vinyl decals, etc. If I didn't get the family discount it would still be pretty cheap. Find out what kind of local screen printing places are around your area and if you've got something in mind they should be able to get you a quote.
I don't have a lot of photos of stuff I've had made, but this is what I could find in the pics i've already uploaded to the forum:
I'm on like my 4th or 5th hat in 10 years, here's one of the earlier ones and my original concept design.
I also created the vector artwork for this vinyl cutout based on a sticker I got from a member of the Ohio Delorean Owners club. I've made a bunch of these in brushed aluminum vinyl and put them on the back of my cars and other random stuff.
Files don't need to be in vector format (DXF, PDF, etc) but those file types are preferred since they can be scaled to any size with no loss in quality. Raster files like JPG or PNG also work, but you'd be limited to the resolution of the file for printing, or if you're having something cut in vinyl it would have to be remastered into a vector file.