The electrical leads for computers, printers, phones etc all contain very small wires, the cables on power adaptors for charging phones, head phones, speaker wires are also a good source. The $2 shops carry a good renage of IT cables for any type of application, it's just a matter of stripping these cables and measuring the internal wires, the smallest I have found so far is 0.07mm with the average size being around 0.1mm - 0.15mm.
Des.