I got this 20mm PO rubber strap from an ebay seller in Asia as no TDs have them in 20mm only 22mm. I tried one from an American seller but that quality was poor and a dust magnet, but this Asia one is very decent quality for $35. It fits pretty tight to the case, maybe a 1mm gap on one side, and is pretty firm and not too flimsy.
I took quick pics so didnt clean the dust off and as its not gen it does take some dust but not too much.
http://www.ebay.com/itm/Restore-20mm-Black-Rubber-Seamaster-Planet-Ocean-Watch-Bracelet-Band-Omega-Strap-/230830014836?_trksid=p5197.m1992&_trkparms=aid%3D111000%26algo%3DREC.CURRENT%26ao%3D1%26asc%3D14%26meid%3D877327056024347679%26pid%
3D100015%26prg%3D1006%26rk%3D1%26