You could always convert to cast wheels.
There are some long narrow round spoke brushes available, but not usually in auto stores. Maybe a Harley dealer?
Something like D or E at this
Link
Seriously, I've not found any easy way to keep spoke wheels clean. I use rags torn into strips about 1/2" wide and floss the spokes.
Polishes?
3M Professional Formula Chrome and Metal Polish Part # 39527 is Great Stuff - In some NAPA stores
Blue Magic Metal Polish Cream, nearly the same thing - in most AutoZone stores
Then there is always Simichrome - Expensive - so I use one of the others first and finish with that, it only takes a small amount to do a whole wheel, including the spokes.
I've also heard great things about Autosol, though never seen it for sale around here.