You might check with Eastwood (http://www.eastwood.com/). They are into powdercoating and may offer a color close or know how to mix it/get it mixed. - Bill
I just had the whole frame from under my '70 GS 455 Conv. done last week at East Coast Powder Coat in Northeast, Maryland. They are about 10 minutes from my house and did a great job on the frame. I degreased it and they sandblasted and powdercoated it gloss black for a very good price. Their website is www.eastcoastpowdercoat.com I dropped it off on tuesday and I picked it up on Friday. They have prices for everything right on their website. Ken