Most of the bowsaws i've seen have split wooden tenons integral to the 
handle, so they have wood-to-wood friction surfaces. I think i've seen 
one where the tenons were tapered.

The one saw with metal pins with which I'm somewhat familiar  is a 
Marples, It has a disc of resilient material sandwiched between brass 
washers on the pins between the handles and uprights.  it should be easy 
enough to try something like that.

Another thing you might try would be apply some rosin to the pins - the 
sort that bass & cello players use.

Don