I scored a beautiful chromed original Yoshimura pipe for my CB750 earlier this month, the owner had it hanging up in his shed for years, he didn't like it because he couldn't use his centre stand.
Lucky for me it hasn't done much work, and is in excellent shape. The older ones like Andy's (736's) were paper thin (to keep the weight down, I guess) and rotted worse than OEM pipes.
Luckily for me, mine is the later version with the straight headers, and slightly thicker material, and it's rust free. The one on my Yoshimura equipped GS1000 literally fell apart when I fired the engine up!
I don't know what the holdup is with Andy's pipes, they'd be simple to make, just using exhaust bends. but Yamiya are selling Yosh replica's, so maybe he's decided it's not worth it? Cheers, Terry.