Contact Miata_B_racing he sold/sells window bushing kits(on eBay) for around $35, iirc, i have bought two kits from Jake, great guy! Profile on m.net:
http://forum.miata.net/vb/member.php?u=79319
Here are his kits:
http://www.ebay.com/itm/Mazda-Miata-...36955c&vxp=mtr
(*verified they are one in the same)
Definitely recommend the kit and a good time to do them when installing these gorgeous Carbon Miata window cranks!