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I believe this is the last aftermarket one left on earth lol https://autoplicity.com/3576635-standard-motor-products-ry547?gclid=CKPN0fGkndICFdgagQod9P4HOQOEM 20006113
check eBayhttp://www.ebay.com/itm/1978-87-Monte-Carlo-Regal-Cutlass-Power-Door-Lock-Relay-NOS-/391693085403?hash=item5b32ba2adb:g:bYcAAOSwImRYWH~g&vxp=mtrWhat's wrong with yours? Remember they are case grounded so they need to be rigidly attached to the bracket by the column.
Are you sure it's not still bolted in?
There's another used one on eBay listed today. You can probably get one cheaper if you pull it yourself from a truck, blazer or suburban. Monte Carlo, Buick etc same relayhttp://www.ebay.com/itm/1978-1987-Grand-National-Regal-T-Type-Interior-Power-Door-Lock-Switch-Relay-GM-/112310307731?hash=item1a26374b93:g:QMEAAOSwx6pYq0cg&vxp=mtr