I'm not quite sure what you mean by "strapless".
All shoulder rigs have a strap or harness somewhere to hold the firearm in place.
Safariland sells a "universal" fit model that you may want to look over.
As for simple shoulder holsters for J frame or PPK type sidearms I'd look at
www.Bianchi-intl.com or
www.Galcogunleather.com .
A concealment garment or undershirt from 5.11 Tactical or Kramer may work best if you want to avoid straps or buckles.
CF