If you need to find some strong sheet metal fast for your workshop, you've got a few options that are generally affordable and easy to handle. One method you can do yourself, while the other two are better off done by a metal shop. Which one you choose depends on what design you're planning for the sheet metal to have as well as the timing of your project.
Reinforcing by Bending the Edge
If you don't need the edges of your metal to be completely straight and you need the piece of metal right now, you can try bending the edge of the metal. Simply folding the edge over and then flattening the now-doubled layers can provide more strength to the sheet as a whole. The thicker edge makes it harder for the sheet to bend unexpectedly. The sheet metal may still be flexible, of course, but that edge gives the sheet a little more reinforcement.
Another method is thermal processing, which is best done by a metal shop. If you can wait a bit for the metal to be finished, thermal processing can make the entire piece of metal much stronger. In general, thermal processing involves heating up the metal and then cooling it, and it's divided into three different types of processing: annealing, normalizing, and stress relieving. Normalizing is particularly well-suited for strengthening purposes because it affects the grain size in the metal. Pieces that have been formed from melted metal form a crystalline structure as the metal cools. The small crystals are called grains, and smaller grains mean more strength. Since normalizing further reduces grain size, the resulting metal is stronger.
Cold working involves bending the metal in certain places and ways. The previously mentioned option of bending the edge of the sheet metal is a fast form of cold working, but, overall, cold working involves many different types of shaping and bending that don't necessarily require the edge of the metal to be folded over. You may be able to do cold working in your workshop if you have the appropriate machinery; if not, a metal shop can help you out.
Metal is an amazing material not only in how it's constructed but also in how it can react to different processes. Contact a metal shop to discuss what you need in your project and whether the shop can create it for you.