Kawish,
If it is a 43mm Kayaba, which I am pretty sure it is, I have a spare 43mm Kayaba off of a 93 YZ125. I bought them on Ebay for the exact same reason as you for my 96 WR250 and I actually used the fork cap off of a friends 95 KX500 until I found that set of forks on Ebay. The plastic guides and several other components are different but the fork cap works. Would you like to buy it off me for like 20 bucks with shipping? That cap is like 70-90 depending on the vendor.