Numrich lists Parker mainsprings for $3.35 each.
Part #136 on their list. Numrich can be hit and miss at times though!
http://www.gunpartscorp.com/catalog/Products.aspx?catid=3745LCS top tang screw ('top trigger plate screw')is sold out.
Popperts lists the Parker springs for $5 each.
http://www.poppertsgunparts.com/I don't see any LCS parts there though.
Also try Valley Gun Shop, West Falls, NY for Parker and LC Smith Parts. I've purchased quite a few original parts from them in the past.
There's an email as well as a phone contact somewhere on their webpage.
http://www.thevalleyguns.com/