2 sided stls are abundant on the net. Thingiverse, My Mini Factory, Grabcad, turbosquid,,,,,,,,,,just to name a few.
You can machine them how you like just takes a bit of work to ready them for cutting in Aspire.
The attached was a full blown 3d model stl I just chose to base relief it.
Google is your friend when it comes to locating models of all types.