I send my chain out for sharpening. They do mortiser chains for several framers that I know of. They do a nice job and will customize the work for hard or soft woods if you deal strictly with one or the other. It's been a while (I need to do it NOW!) but the address is:
Miller Sharpening
11301 Webb Ave.
Alliance, OH 44601
330-821-6240
They're pretty quick too. You'll usually have it back in 7-10 days.
Any spray lube will work as long as you're not using so much as to make it gummy of spattering the timber. A little shot of CRC or equiv. every couple or three mortises should give you what you need. Unless you're being really hard on it and working fast, the chains don't get particularly hot. Good luck.
