Optima parts come up all the time on ebay. here's a search for "optima arms"
http://shop.ebay.co.uk/i.html?LH_Ava...arr%3D1&_rdc=1
Unfort, lots of it seems to come from overseas and is expensive.
Also try a want ad here on oople or just watch the for sale section. I picked up a huge bag of optima parts a month or two ago for a very fair price.
Cheers,
Ty