Original Precision and TK Customs both make internal lock plugs for S&W revolvers (in several different finishes) for about $40.
I only have a few "modern" revolvers with the infamous lock...2-5/8" PC 627-5, 1-7/8" 642-2, and 3" 686-6 Plus. So far I've been able to ignore the internal lock (and I never use it!), but I may plug a couple of my revolvers sometime in the near future.
BTW: By picking up that 386PD, you've got a tiger by the tail! There's a reason that it was "cherry" and reasonably priced...those Sc/Al frame and Ti cylinder revolvers kick like an Army mule! I had a used one for about a year (with aluminum carry case, etc.) because I thought the 7-shot lightweight revolver would be an excellent EDC. I am not recoil averse (I routinely shoot .44 Magnums and hot .357 Magnums in heavier frame revolvers), but that little L-frame was too much for me. There was too much recoil to allow for fast follow up shots, and it just plain hurt my hands. I hope that it works out for you because they are cool revolvers. Enjoy!