Don’t know if others know, but I just found out that aluminum gauge is different than steel gauge.
http://www.custompartnet.com/sheet-metal-gauge
Not knowing what your project is, I’m not sure how important the difference might be.
Since you also state .030" that will be the same for any material.
Some suggestions without solid research, and really just to spitball:
- the HAAS discard barrel sometimes has stuff this big; the practice bin may, as well, and I think either of those are fair game.
Some things which might work, but I can’t find their thickness (stated authoritatively online, a person would have to measure):
* Aluminum can bottom (you'd have to flatten it, and I have no idea how thick they are);
* aluminum [gutter pieces](http://www.homedepot.com/p/Amerimax-Home-Products-5-in-White-Aluminum-30-Degree-Right-End-Cap-5ENR30W/205604986?MERCH=REC-_-PIPHorizontal1_rr-_-205627125-_-205604986-_-N) (no idea how thick they are);
* aluminum [tubing](http://www.lowes.com/pd_121641-85334-VTL0001_1z0vj5n__?productId=4129922) for dryers, etc.
* chunk of a cheap-ass frying pan (no idea how thick they are, but the cheaper the better for this purpose).
Several things could be used if layered/epoxied together:
* layers of aluminum can;
* layers of [aluminum flashing](http://www.homedepot.com/p/Amerimax-Home-Products-10-in-x-10-ft-Mill-Finish-Aluminum-Roll-Valley-68310/100054269);
* layers of [this](http://www.homedepot.com/p/MD-Hobby-and-Craft-6-in-x-9-in-Aluminum-Sheet-57507/205833444) 6"x9" sheet from HD