Clark Custom Guns is selling original factory 10/22 metal trigger housings for a very fair price. Apparently, they bought out Ruger's remaining supply when Ruger made the shift from metal to plastic trigger housings for the 10/22. I have one coming...will order a couple more if it looks to be in good shape...
http://www.clarkcustomguns.com/RugerOEMtrigger.html
http://www.clarkcustomguns.com/RugerOEMtrigger.html