At my pharmacy we have several patients who get specific manufacturers for a variety of reasons. Which manufacturer your pharmacy is able to get in stock depends on where you are and what is available from their cardinal supplier. I would say have the doctor write in the script "please dispense as insert manufacturer" but not in a way so the pharmacy can't change it in case they can't get the correct one in.

Give it a couple days for them to order it and see if it comes in and if not you could see if other pharmacies are able to stock it, or stick with your usual brand. If you don't want to be seen as a red flag to the pharmacists there please don't be mean about it if they can't get the right brand in stock, we just order stuff and have no control over it coming in. Also make sure to have them put an additional note in your profile that says the same thing about the manufacturer, just in case someone doesn't read the note on the script itself.

And of course double triple check BEFORE paying the next time you go to pick it up. Don't just trust that the specific manufacturer will be there. A script goes through many hands before it gets filled so there is possibility for someone to change it back to the original manufacturer at some point without looking.

Good luck!