I'm not terribly familiar with the system, but GURPS tends to have a wide range of sourcebooks. (I myself picked up several from their historical line for my Mythic History game.) GURPS Steampunk would be my first thought. There's also a "Weird Science" chapter in their Weird War II sourcebook. The Deadlands game also has the same sort of pseudo-science aspect to it, and has been published in the original system, GURPS and d20.
A random source of steampunk inspiration is the
Steampunk Lab.
There's also this free preview of GURPS
Warehouse 13, which going by the ToC seems to have a lot of weird science elements to it.