Where is "here"? The 258 is also known as the 4.2L and has been used in AMC cars as well as Jeeps since the mid 1970s. Unless you live on Mars, I can't believe there aren't any used ones in your area. However, you might have to buy an engine to get one -- but if you find a junkyard in your area with some AMC cars, ask if any have a blown 258, and if so ask if you can buy just the crank.
If you want reconditioned, check all the chain parts houses -- Auto Zone, Pep Boys, Advance Auto, Checkers/Shucks, NAPA -- for a 4.2L crank kit. They all should have access to them.