I've done the skateboard bearing mod using cheap bearings I got off eBay. They don't really spin in the end of the linkage so it's not important how "high end" the bearings are. The rod will rotate within the centre of the bearing anyway so you're not really using the bearings as they are just working as a bush.
I had a hard time getting mine to fit, but managed to press them in using a G clamp. Apparently there is a smaller size bearing that pushes in easier but as far as I know skateboard bearings only come in one size.
Also, you might need to pack the linkage with a few washers, unless you manage to get two bearings in each - I found this too difficult and just used washers.
Overall an awesome easy mod, makes shifting so much nicer.