I don't know of a mod that does exactly what you want. Have you looked through the mercantile category in the files section? There are some mods that add new weapons and armor to the merchant lists but I'd bet they're still leveled. You seem to be looking for something that "unlevels" the merchant inventory list. I don't know if this has been done. You can look at the mod "Unlevelled World
" but that removes all leveling in the game (for spawns and enemies i mean) so that may do more than you want, and it may not even touch the merchants, I'm not sure.'
Edit: added link to mod and can confirm it does what you want with the merchants, but also much much more that you may not want. It's not modular either but talk with the mod author and maybe you can figure out how to do it yourself (if you can't find another mod that does what you want).
Edited by thompsonar, 03 August 2012 - 12:43 PM.