The easiest way is to buy a normal rug that you can cut down to size to fit your shape. Rugs made out of synthetic materials are easier to cut since they do not need special processing to stop them from getting unthreaded. You should draw an outline on the back on the rug and use a very sharp cutter to trace it. To prevent damage while cutting, you can put a regular kitchen cutting board under your work area. Finally, you can seal the edges either by singeing them, putting a bead of glue or buying adhesive rug edging tape.