you can apply to companies like autocad that design software programs for mechanical engineers. there are quite a few mechanical engineering software companies and programs. typically these ME software programs will perform, thermal analysis, dynamic analysis.
im sure you will find once your at work you will be constantly writing software, and/or working on a workstation. a lot of these mechanical software engineering companies are located in silicon valley or on the eastcoast.
in addition large companies will sometimes have their own internal software designs programs for in house mechnical design programs. so you can ask to interview in such a group. i wouldnt worry to much when you start work you will find you just naturally have to use or write a lot of software if you work on advanced design problems.
heres a typical small company that produces some specialized mechanical engineering design software, they would probably LOVE, to have someone like you. i used to supervise mechanical engineers and they are typically not good programmers, so your skill set should be demand espescially as finite element modeling and other computational ME aids come to the forefront for advanced design.
in todays world 'hardware" is software so to speak.
good luck in your new career.
http://www.hexagon.de/