I
love the idea of old G1 comic covers on clothes!!
...that's really limiting.

Has Hasbro casually forgotten that G1 spanned from 1984 to 1993!? (-_-)
Anyway, if you need a quick reference for G1 (and G2) covers I recommend this site:
http://www.tfarchive.com/comics/marvel/
As for other characters on that list:
Optimus Prime
#331
#300 (you might need to ask Hasbro if you can feature those other Autobots, or creatively remove them)
#177
#106 - Optimus Prime vs Megatron
US#24 is the same image w/ different colours and text
#100 - another Prime vs. Megs; you'll probably have to remove background characters
UK#70; probably need to remove background characters
UK#29 - Prime v. Megs
UK#4/
US#2 - Prime v. Megs
US#42
US#71/
#311
#321 - may need to remove Scorponok
#322
G2 US#1
Bumblebee
UK#3
UK#58/
US#16
Grimlock
#111
UK#32
[url=http://tfarchive.com/comics/marvel/covers/uk325.jpg]#325] - may need to remove Fangry
G2 UK#2
1991 Annual - remove background Dinobots
Megatron
#244
#98
UK#51
UK#8 Megatron pwning Prime
US#48 - will need to remove background characters
1989 Annual - Megatron v. Prime
...and if Hasbro will allow Galvatron to count as Megatron:
#202 (Megatron back to back w/ Galvatron)
#199
#173
#118
#101
US#67 -
illustrated by Jim Lee!
G2 US#5/
G2 UK#4
G2 US#8 Prime and Megs back to back
G2 US#11 w/ Prime and Matrix-powered Starscream
Starscream
US#50 - Underbase Starscream; if you want an image of him w/o those other Transformers try
#208
US#9/
UK#34
US#49 - will need to remove background characters
Devastator
UK#36/
US#10
...and if you're allowed to use individual Constructicons:
#UK61
Jazz
1990 Annual - remove background characters
This cover features Jazz, Grimlock, Bumblebee and Starscream!
This cover features Jazz, Bumblebee and Grimlock (discovering 'God'

)
...that's all I can think of. Just click on that first link I've provided and you can browse through every G1 and G2 cover.
P.S.: Oops, forgot about Soundwave and Hot Rod - again, you'll find covers with them on it on that site. (^_^)