ER shows up usually about once a month or so at the big box liquor stores. Most usually do store picks as well, but that’s only a couple times a year those will show up. Some will put them out on the shelf (like Total Wine) while others may keep them in the back and only give them out if you ask for them (Twin Liquors usually does this from my experience).
The only chance you have at getting any Weller product other than Special Reserve is to get lucky during the annual Buffalo Trace/Weller drop. This is the usually once a year drop that Buffalo Trace does that will include a few ETLs, Weller Full Proofs and CYPBs and a few cases of OWA and W12. It’s my understanding that the big annual has already happened this year, so you probably aren’t finding those products at MSRP any time this year.
Blanton's, Eagle Rare and Buffalo Trace usually get dropped once a month. You’ll have to learn when your stores get their deliveries (it varies by store) to keep up with the flippers (who snatch up Blanton’s all the time because it’s an easy sale and they can double their investment).
My best advice is to join local Facebook bourbon groups and that will hopefully tip you off when the good stuff is at least in your area. That way you can ramp up your hunting efforts at the right time. Being in these groups tipped me off when the big Weller drop happened and helped me snag BT Kosher Rye recipe, Weller Single Barrel, W12 and OWA all in the same week at MSRP. I’m just a regular dude like the rest of us here and not a flipper (who typically give kickbacks to store managers or employees for tips on when the good stuff is coming). Being in these local groups is about as good of a chance as you’ll get to having a chance at landing these allocated bottles.