Methylcobalamin is making it into stores locally now.

Walgreen's has it. Costco too. And yesterday we were in Sam's Club and they even had it.

If you use it sublingually you must still do so on an empty stomach. Most of it that dissolves in your mouth, is in the saliva which you swallow. That can be absorbed passively in the intestine if NO FOOD is present to block it. Sublinguals are really historically offered, but really do not provide much B12 that way. The B12 is in reality absorbed dissolved in the saliva. Recent studies show oral and sublingual equal in effectiveness (so take on an empty stomach so that presence of food in the GI tract does not block the microgram amounts of the B12.)

The nutrients you list as low for you are dependent on stomach acid for absorption. If you take acid blocking drugs frequently or if you have a natural achlorhydria, which many people develop in life with aging, then low acid means you can not absorb nutrients that require acid.

Betaine HCL is a supplement that helps restore normal acidity in the stomach for people with achlorhydria.
At least 600mg with meals (up to about 2 grams if needed) is the typical dose. This should be discussed with your doctor.
As should long term use of acid blocking drugs. Many doctors do not attend to the long term negative consequences of lowering stomach acid.