Last time I made a shirt I used CustomInk to do it...it was not too expensive and you can design your own shirt with uploaded images using their online "LAB". I suggest you use this link to make your own design:
https://www.customink.com/lab
When using it you can even add your own name on the back or I was thinking the number "35.5" or "35.5 MILES", etc. I'm guessing it costs extra. I think you can also choose other shirt colors - instead of just white, etc.
Here is a screenshot of a couple of possible versions - using the "non-background" version of the images I made:

And here is what it could look like if you choose the one with the background - which would be a big square - doesn't look as nice, in my opinion.
(Note, I can remove the blue lightning bolt from the background too, and just be GRUMPY by himself with the text)
If you want different variations/colors (in text, etc) then let me know. I will upload the various pictures tomorrow but you can get an idea of the options I thought of so far. I thought about adding Donald Duck like someone had shown in a different design, but that might just get cluttered.
Also, there are probably other websites that can also make these shirts for you (like cafepress.com, etc) - in case CustomInk won't or in case you have different preference.