When you're retired, and don't need the funding, there are plenty of under- or un-funded research projects that can be done. The right professor would likely be open to collaboration/guiding work like this, particularly if your PhD augments the skill set of their group/lab. You don't need them necessarily, but it might help to bring you up to speed with publishing (assuming that's your goal - and if you're doing research, I think it should be. You want the work to persist after you if possible). Proposer and funders are pretty good at figuring out good use of limited resources, but they just can't fund everything and there are many un-turned stones.