Four Springs needed

Based on some very detailed, expert advice on my Zink Z-16 (coming along slowly and steadily), it looks like I need stiffer springs fore and aft.

I need two springs 6" x 2.25" x 800-1000lb (but both must be the same)
and two springs 8" x 2.25" x 900-1100lb (but both must be the same)

I know where I can get them new, but I'm on a tight budget so looking for used, first.

I will have to make a determination in that range based on what's available. I think I need a spread of 100-200lb but could also do with less if all four were 900-1000lb springs.

Thanks!
David

Four Springs needed