Depending on your application there are various place to purchase your methanol. If you are using a 50/50 mix, various companies sell this premixed. The issue is shipping charges can double the cost of the product making it impractical.
If you are looking for pure methanol, then we have put together a few links to help you out. Please read the Alcohol FAQ before getting contaminated methanol and using it in your system.
First, most places that sell race gas can order in methanol in 5 gallon pails for you. You can also check the local motorcycle shops, boat/powersports shops, even engine rebuilders and dyno/tuning shops.
Make sure you are getting 99.9% pure methanol, no additives.