Recipes can be bought from Basil at Clockwork Terminals/Bazaar, from Hall of Heroes, at the beginning of certain missions, from Krogmo in Arcade, or from Auction House.

Some minor notes:
Recipes bought from Basil at the Bazaar only go up to 2*, and he only provides a small selection of recipes at a time, so you may need to do several recipe runs if you're after a specific 3* or above recipe from him;
Recipes from Hall of Heroes automatically come bound and cannot be sold to other players, not to mention that boss reward line, Graviton Vortex line and Krogmo recipes are unavailable in this fashion;
Recipes from Krogmo also come bound and cannot be sold, and require a certain number of tokens rather than pure cash;
Mission recipes will only have a few available, much like standard Basil;
Auction House recipes are often priced at higher than their original purchase value.

Hope this helps.

Edit: Some recipes are now awarded as mission rewards, so you may not wish to purchase them since you'll get them eventually. The notable (3* and above) recipes are: the entire basic weapon/armour set (Solid Cobalt, Great Defender, Super Blaster, Tempered Calibur, Super Blast Bomb and their 4* and 5* version recipes), Shadow Driver, Plasma Capacitor, and Strike Needle.
Also, all crafting has an energy cost that increases drastically as you go up to higher-starred equipment. For gear of 3* and above, you'll need to purchase CE somehow, either direct or from another player.