I had a very similar problem as yours. I'm assuming you've checked for off-the-shelf sprockets at McMaster et. al.
I went to Maryland Metric.www.mdmetric.com
They will bore any sprocket to any shaft bore. If you need, they will cut a keyway and tap for set screws as well. I had sprockets made for about $35 apiece.
BTW, their web site blows. But in the end I got a perfectly machined sprocket that fit perfectly.
Also, I found a couple of 8mm bore #35 roller chain sprockets at Stock Drive www.sdp-si.com
. But they're acetal resin (not steel) and there's only a couple of sizes. It might work for you, though.