I've posted about MicroMac before on this site, but many of those posts were lost one year ago when we had a hard drive crash. (And as we celebrate the anniversary of that crash, I sincerely hope regular backups of this site are being made so we don't lose everything again.)
MicroMac is out of business, but the fact they have left their website up is nothing more than a sheer act of deception. Yes, I've written them before. Still have their email replies to. But that's from a couple years ago. Now if you write them, no one will reply at all.
But not to worry, you can still buy some MicroMac products such as the Diimo 50MHz 030 PDS accelerators here in Japan. Have a look at my
DiiMO photos on Flicker. Click on the topmost photo and read through the comments I've posted. Toward the bottom I've given you all the details you need to know about where to buy. And yes, I bought my DiiMO from NEXTRO Japan.
Getting back on-topic, I don't know if NEXTRO sells the Mac Plus upgrades, but you ought to ask. They just might. And if they don't, they will be happy to sell you a Classic or SE that runs OS X Leopard, with an LCD color screen too!