Scour building plan sites that offer stock plans to find one that fits your footprint. If one comes close, many of those companies offer design services to alter their plans. Have them alter it to match your foundations rather than let a builder try to do it from a stock plan.

If that doesn't work, find an Architect.

If you haven't done so, start with drawing up an 'as-built' drawing of the house so you can see what is possible.