Sure Shot or Galvanized Shot

Barrel Diffusion or Galvanized Diffusion or Amalgam Barrel Diffusion

Pistol Gambit or Primed Pistol Gambit

Target Cracker or Primed Target Cracker

Frostbite and Pistol Pestilence give you viral, but you can swap for other elemental mods to change type

Scorch or Primed Heated Charge

Scorch gives a higher status chance (over 100% gives extra procs per shot) at the cost of lower overall damage, however, the weighing should give roughly 25%/25%/50% slash/heat/viral.

Primed Heated Charge gives higher overall damage, but makes the status weighting more 30/45/40 slash/heat/viral and you lose the extra procs per shot since you are below 100% status chance.

Extra Note:
If you don't care about heat (which isn't likely since it strips armor), you can try Carnis Stinger for a 50/50 slash/viral.