I don't know of any retail sources. You could consider finding someone who sews to make you some. I don't think it would be too hard to make. I've sewn some pillows and a few different things myself. You can go pick out the material and cushioning yourself with help from the person who is going to sew it and the sales people are usually pretty knowledgeable on materials. Let them know what you plan to use it for and probably want it fire resistant material. You could use another pad for a template/pattern or the seamstress could probably just take some measurements on your harnesses and come up with a pattern. Ask some relatives who sew or visit a senior center to ask if someone would like to make one for you. It would be cheaper than contacting a professional seamstress or maybe even free labor plus cost of materials. You could end up with a nice customized comfortable fit for yourself.

You could also exchange your car skills for someone doing the labor on the sewing project. I bet an older widow would appreciate that.