Ahoj Srdjan! Unfortunately, I do not have a spare J3. I just received mine, in Kiev mount, about one week ago. I paid it 59$ including shipping on eBay, from seller gutphoto, located in Dnepropetrosvk, Ukraine. Despite having a rating of 97.3%, I decided to risk it, and I got a winner lens, perfect in all things. I decided to go after a chrome Jupiter-12 from 1958, looking similar to the biogon and produced at Arsenal. If I ever find a J-3 here in Prague, I will let you know, but those are pretty scarce here. I've seen some Orion 15 and Russar MR-2, but they are expensive as hell!
If I ever find something I'll let you know... but I think it's going to be a difficult task.