I have a set of 24" cruiser wheels with redline hubs. They have threads on the other (left) side of the hub also, but the outside diameter of the threads is smaller a normal shimano freewheel.
I assume these are flip flop hubs.

Can someone tell me where I can find a 17t sprocket in this smaller size.

I see an ACS freewheel on aebike.com that may fit, but only in a 14 tooth size. (I really want a 17 tooth). Here's the description from aebike:
ACS
ACS Fat Freewheel 14t 1/8" (FW1234)
$16.49

Specifications:

Chain Width: 1/8"
Color: Brown
Teeth: 14
Thread: Metric (flip/flop), 30x1mm

thanks.

I believe the only freewheel you will find to fit the other side of your hub is a 14 or 15 tooth.