Actually, your not wrong at all, that is very good advice! Planning ahead like that can save a lot of time AND frustration.
I don't know the answer to this one. However, I can imagine strolling into a pharmacy and saying, "Hey, 'got any methadone," and the pharmacist saying, "Erm... no."
So, what if you knew you were going to be getting a methadone prescription, and you visit the pharmacist ahead of time and ask for the Main Lead Supervising Head Pharmacist (if they say "Oh he/she won't be in until monday, then by all means WAIT 'till monday!), introducing yourself, letting them know you will be seeing such-and-such a doctor, and you were wondering if they need to pre-order your medicine...
Kinda like planning "ahead of time." Pre-planning, so to speak. Understand there are LOTS of drugs pharmacies don't routinely stock. For example, those super-expensive rare treatment medicines. So what would a non-pain patient do? Well, you go in ahead of time, and make arrangements. I would think this would work for methadone.
If I'm wrong (and I'm usually wrong about, well, just about everything), please post your comment!
You could also try a small mom and pop kind of pharmacy also. A lot of those might not have them in stock, but if you are their customer they can usually order them for you regularly.
Have you tried Walgreens? In my area, they carry everything.
Also, ask your doctor's office. They may have a pharmacy with which they work.