I assume you might like a Motorola such as the
M2-RN-T12-1LL-120. Unfortunately mine both failed though I was able to get the comparable Sylvania model as a replacement. Although not vintage, I'll note that the GE
GE240PSMVN-DIYB has nice slow startup, so that might be one to keep an eye out for. Unfortunately I don't have much in the way of extras myself, though if you have any interest in magnetic rapid start ballast for 2xF40T12, I have lots of those.