Buying the Roper plate means you've at least taken "mental possession" of one. Good on ya. Decide which model or range you want, and begin the search. You could get lucky or it might take some time, so be diligent. I've watched the market pretty seriously for several years. Cycle Trader, and CL Search Tempest mostly, monitoring classifieds here and Wild Guzzi. There are periods of feast and of famine. Having a low production number to start with, combined with price and condition variables, it can prove tough to find the one true love. But, it can be done. Bikes with issues can be 2-3k$, and the "collector" versions can hit 10k on the high end. I feel comfy saying you can still find a nice example @ 4-5k.
I have ... 3 times.
Anyway, welcome to the forum. Good luck on the search and the find. Keep us posted! We like pics!