These guys seem pretty reasonable and they can do a flap holster if it's for work and needs to be worn over the jacket,
http://clarkforkleather.com/leather-chest-holster/
Simply rugged has a chest adapter as well for their sourdough holsters.
Lot's of options for the 4.2" Redhawk, here's another http://www.diamonddcustomleather.com/Chest_Holsters.php