I've always figured the Seattle branch of PHI is no more than 25 people, most of whom are support and administrative staff; it's even possible that "the cast" is the entire investigative part of the company. I haven't quite decided. :3 Sol and Shiloh work at the Seattle office; the titular Priest and Hawthorne live and work elsewhere.

The firm is very much a private company, however there are some perks in working for them. The company itself provides the silver bullets, and they are provided in various calibres "as needed," whenever stock runs low - despite the fact that nobody at the Seattle branch ordered them. You may eventually find out what mechanism drives that. Employees are not charged for the rounds, and can use them whenever they like -  however, Sol is also likely to know if someone grabs a handful and sells them for the weight of silver. Nobody has, however, done that for many years.

Edit: Sorry, I missed a question. As far as the actual composition, generally-speaking I've figured they're elemental silver metal sintered in a polymer matrix with a nickel-silver plating, jacket, or driving band, available in ball and hollow-point depending on the employee's preference. I haven't actually done the metallurgy to know if nickel-silver would [i]survive[/i] that, but until I get my hands on that kind of equipment again I'm basically going to handwave that and say [i]deal with it[/i]. :3 Shotgun rounds are sintered-silver slugs, silver shot, silver shot packed with silver nitrate, or some kind of phosphorous "dragon's breath" round. 

I generally assume the characters themselves have their own contacts capable of creating "mystical" silver ammunition - casting silver from family heirlooms or holy objects, or inscribing runes or sigils of power onto them. If one of the characters in the "possible last slot" pile becomes a character who can make these, this story will change slightly.

For snooping equipment, the company has a couple of sets of several-generations-behind-cutting-edge law-enforcement grade equipment - directional microphones, fiber-optic cameras, things like that. More modern equipment is up to the acquisition or creation of the individual employee, who can probably expense some of those back to the company. Basically, this is a narrative cover-all for "if you actually need it and it's not absurd, you can probably have it."

As far as weapons are concerned, the characters are free to pick and choose their own. The company does, however, have "recovered" weapons from previous cases that are locked up in Shiloh's archives, which you'll have to ask her to check out. If that ever becomes important (Or someone really just wants to know OOC), we'll find out what's in there.

I hope that helps! :3