49 3600 - S-10 Swap - 8 Lug Wheels

[mr48chev]

You might try these guys for adapters. http://adaptitusa.com/index.aspx They don't show five to eight lug adapters because I would imagine that there is very little call for them. They do say that they do custom orders.
They may snicker a bit as it won't be a common request but my guess is that it isn't a difficult request when they are already set up to do both bolt patterns on their adapters.

I think a lot of the guys with the S-10 chassis in these trucks are using a 1-1/2 inch spacer to space the wheels out in the wheel opening anyhow as the S-10 track is narrower than the AD truck's track. That might depend on how deep your rims are though.