Welcome to Librarium Online!
Do you know if their are any rules for inquisitor fleets?
Kill one man you're a Murderer.
Kill ten you're a Monster.
Kill a hundered you're a Hero.
Kill a thousand you're a Conqueror.
Not as such, no. There was a Grey Knight Strike Cruiser made by Forgeworld but it used the same rules for normal Strike Cruisers. Inquistiors can commandeer any ship they feel like so long as a more important Inquisitor hasn't already done so.
You mean Inquisition fleets, I assume ^^
There's no proper fleet list, if that's what you mean.
There are experimental rules (as well as a conversion guide) for making and using an Inquisitorial Blackship (basically its a smaller & cheaper Battle Barge, but it hits almost as hard).
There are also rules for using the GK Strike Cruiser that are different from standard SM Strike Cruisers, but for the life of me I can't remember where. I'd assume in Fanatic magazine, but most of the articles from Fanatic are on the BFG website already.
Like monsieurcartier said, though, Inquisitors have the power to commandeer any vessel they like, so just build an Imperial Navy or Space Marine (don't steal a Battle Barge though, even an Inquisitor's authority only goes so far!) fleet and call it the property of the Inquisition.