The RM-LG112 is going to be hard to find, but simpler replacement remotes are available for $50 or so. Is the receiver you bought a STR-DA1000es? If so, or it's a STR-DA2000es or 3000es then you can use a variety of universals, but not all button labels will match the names Sony uses. Most of these universal remotes will be set up to use AV1 mode, while there is a good chance that the receiver is set up for AV2 mode. Instructions on how to switch the receiver mode.
If you want access to just power, volume, etc. then most universals will work. To be sure that it will work, get a RCA RCRP05B, or e.g. the Comcast cable remotes. Use setup code 0158 (30158 if the remote takes 5 digit setup codes). Post back if some functions are missing-- these particular remotes (and others made by UEI) can have each button manually programmed, and we know all of the function numbers.