Custom cover creator here. I have a cover ready to honor the 75th anniversary of Jackie Robinson's first game. I would like to maximize the meaning of the date cancellation and was wondering if anyone knew if a baseball stadium (Coors Field for me in Denver) has a post office?
I've seen many sports related covers with cancellations at "stations". How are these stations established? I've seen them for a stamp show as well. These must be temporary and somewhat unofficial. Just curious.
You can phone Coors Field and ask, but I feel it is doubtful a very seasonal facility is going to have a regular post office.
The stations you refer to with pictorial cancels are for specific events and involve temporary offices. They are indeed official and require a USPS post office and personnel on site, which the USPS have to agree to provide. There have been a small number of non-postal/fake cancels, sometimes applied to covers when the USPS has pulled out of participating in an event.
Check out the most recent USPS Postal Bulletins for upcoming pictorial cancels. Ones that passed with no prior announcement can be had for a short time afterwards (which will get mentioned in the bulletin), but those cancels may not have a date when requested posthumously.
"Unfortunately we do not have a post office at the park. The nearest is only 5 blocks away at 951 20th St · (800) 275-8777"
Cooperstown is a dream goal for sure. I usually cannot get post marks outside of my locality for covers like these. If I had planned it better, I would have sent the cover to Brooklyn with a self addressed stamps return envelope. I tried that once though and the post master cancelled with the wrong date even though I sent a letter with all the details.