You can either have a plumber relocate the drain pipe so that it will line up with a shower base that you would buy from the store (usually fiberglass), or you can lay a new and custom built shower base made either out of metal (not recommended) or out of concrete.
They also make showers with off set drains just because of this delima. Don't be surprised if plumbing supply doesn't agree get online and start looking, they are out there.
If you can't find a shower base that matches up your alternatives are expensive. This is simply the most critical aspect of your shower. If installed improperly it can become a leaking, floor rotting, stinky mess. It must be level and have the correct pitch toward the drain. And where the walls meet the base is critical as well and must be properly installed. A good shower base and wall installation can last many years, poorly installed you may be ripping it out nearly as soon as you put it in.
Unfortunatley how to do any of these options are simply too long to go into here, good luck.