I love using this rifle. The issue is, I can't get anyone to repair it past 51% (I think Donovan can fix it a little higher but may be wrong).

Is there any way to get it repaired more minus using a cheat code, giving myself another one....... or six and repairing it myself (repair is set to 100)?

Fully invest in Wolfgang, and he will have 75% repair.
Reverse pick pocket workman's overalls on Moira, if you crush her dreams, this should boost her repair to about 65.
Visit Haley's hardware and exploit the glitch that lets him repair to 100.

All that said, I don't use these methods.

You could play Mothership Zeta and use Somah, although she disappears after the quest ends so that's not a good long-term solution. As it's unique you can't get another copy to repair it yourself, so your best bet is to invest in those Canterbury Commons merchants and boost their repair up to.. I think 79% is the highest. If you don't mind exploiting Haley's bug, you might also want to consider the player.srm console cheat. It's not really that bad a cheat, just lets you repair your items without the need for a second copy, but based on your repair skill.

A glitch on Haley's hardware? What kind of glitch?

***SPOILER ALERT*****

Sorry I haven't been posting long and am too lazy to learn how to add those 'spoiler' tabs that hide your tips.
But seeing as we are on the tips pages and the game is old enough, hopefully I won't get booted off for just writing it.

Every time you visit Haley, his clothes ( red racer jump suit or something? ) add the +5 to his repair stats.
Visit him 10 times or so and 'hey presto' he can repair your T51b armour ( or Gauss rifle ) to 100% with nothing more than the empty popcorn and drink cups blowing around the board-walk, glued together with the tears of the orphaned in-bread children who's parent's hideously mutated heads I separated from their deformed bodies heheheh

As mentioned above, MZ can be useful, the Alien Epoxy can be used on any weapon and from memory, I collected somewhere between 100 & 200 from my last play through I think.