my front brake keeps going spongey and have managed to narrow it down to the master cylinder. For the life of me i haven't been able to find either a replacement or a rebuild kit, does anyone know of a place or if anyone's got one knocking around.

Try Wemoto .. I don't think they're much different from other Yam stuff but then again ...
If I had to say a similar bike if look at the FZR600R Foxeye, the disks are the same but its a heavier bike

I think the genuine kit to rebuild the front master cylinder is part number 3TJ-W0041-50 (as per page 179 of the parts manual). You should be able to order this anywhere which can supply genuine Yamaha spares. Get yourself some red rubber grease too.

If this is no longer available then try 4DX-W0041-50 as this is the identical bike but UK spec.

Chris

I've got a few knocking around in the garage, I've swapped over to radial cylinders.

I use a radial too