Extra or new licence for old version parallels desktop v 10

Hi .. I'm an old user of PD v10 on Yosemite and want to use PD on another Mac of similar vintage. Since I can't buy another box set anymore, how would I go about buying / licensing this other machine please ? Thx

 

Hello,
we stop selling previous version of Parallels Desktop once the newest one has been released. You can find previous Parallels Desktop version on Amazon or ebay for example..