*Suggestion*
1. Basic mod. Add in an Anti-Armor (Gauss) Rifle. Huge AP cost, like 7AP. Big Strength requirement, like 7. Use MF cells to power shots. In fact, it's basically plasma rifle with more AP and reskin, change to use BG instead of Energy.
Add in an Anti-Materiel Rifle. Huge AP cost, like 7AP. Big Strength requirement, like 7. Use MF cells to power shots. In fact, it's basically sniper rifle reskin, change to use BG instead of Energy.
AMR is available in Toxic Cave's ground level locker. MF cell availability will be the limit factor in early game (only early source is Smitty's random restock).
AAR is available in Gecko's Poseidon Plant, one among many lockers. plus one in SAD's courtyard level armory.
Another place is the Klamath's vertibird location. Good, logical, place for a free weapon.
2. Advance mod. Require messing with new critters in random encounters. Maybe more perk but I dont know. Robot armed with these weapons, but set to not drop upon death.
I experiment with Pyromaniac+Flamers and it's not bad.
*Problem*
In Fallout 2 Big Gun is not as viable investment as in, say, Fallout Tactics.
The earliest BG weapon, Flamers, you can get at Redding in Morton job. Problem is, it's level locked. If you are, say level 6, you wont be able to be Sheriff and arrest that bugger to spawn that encounter. same deal with buying from Elridge, because he's level locked behind Made Man status, and that one require much works, thus when you get it you are no longer early level anyway.
The other way for early level character is to travel to NCR via Redding-NCR caravan job and shop there. This is a bit meta, you understand~
A really scary way for early level is to farm specfic Random encounters.
++travel Redding-New Reno. Try to spawn a Claim Jumpers versus other groups, and wait until CJ get killed and we pick up the loot.
++Travel around Broken Hills. try to spawn Unity patrol versus other groups. After that, you can pick up the loot. Or you can murder one of those friendly troopers and run to the exit, which is quite scary, considering their tendency to throw Rocket around like free candy.