I get B12 and B100 10ml from Vitamin B12 Direct. 1 part B100 to 3 parts B13 IM/weekly. The thymine in B100 boosts the release of energy from fat cells and amplifies the effectiveness of B12. Really made a difference for me almost immediately.
B12 Direct is in Thailand, so it takes about a month and costs $10 to ship. Ppl I got the info from have been ordering from them for years and never had any issues. The quality is excellent, which for B12 is important because many overseas vendors pass off poor quality B12.
However, the advantage is the price. I ordered (3)B12 and (2)B100 and they included a free bottle of B12. So, for $75 it will last months. If you want to go that route, they are a tested contact.