Does anyone know where I can purchase 6 underfolder receivers that would work well with the polish kits?  

DPHarms.com had these but they are on back order.    Scott won't have an eta on this until later this week.



are the ones sold here any good?

http://www.nodakspud.com/page2.htm

'Instante':

The DCI receivers you refer to are designed specifically for the Yugo M70 parts kits. The DCI M70 receivers are not a good choice for assembly with Polish underfolder AK kits. The trunion and rear block from the Polish kits will not fit the DCI M70 receivers.
The Polish underfolder kits can be assembled with AKM receivers. If you cannot find a receiver with pre-drilled holes for the underfolder stock parts, you can fit the parts to a receiver shell and make your own holes.
We expect that DCI will make AKM receivers and it is likely that a version for the Polish underfolder stock kits will be offered. Look for this receiver in February.
Thanks.

Harlan

Ok, I will be your first customer for the akm underfolder receivers.  Thanks Harlan.  BTW I think it's really great that you can put our kit serial number on the receivers for no extra charge!  Thanks, can't wait to do business with you, heard a lot of great things!