How would one derive a terminal value for an asset that is brought to market once every 5-6 years instead of annually as I believe a FCF model would assume annual cash flows to derive a terminal value in a DCF model.

I don’t think I can use a Budget/Project type NPV analysis because that assumes the project ends, but in this case the CF are into perpetuity

Not sure if you’re looking for an academic answer or a practical answer, but I’d approach this with a spreadsheet DCF model where you do the modeling for a forecast period of 50 years or so. For the terminal value, you can assume some annual average. After 50 years the discount factor will be so high that the impact of your terminal value assumptions will be low.

Yeah, that’s what I was trying to avoid, but it looks like that maybe the only solution