GDI's (Goodman Distribution Inc.) in my region sell them. They are great for the landscapers and make it easier to service the units when they are up off of the ground. Also, no varmits live under the units when they are mounted like that.
Although I prefer ground mounted units... we have these type of frames built at a local welding shop. We prime and paint ours Black, but any color will do. We use six concrete anchors (3 on each side). Some customers want them on their Wood foundations, so we lag bolt them on with big ass lag bolts... but it's a pain to find the studs especially after the parging is done.
When we set the condenser on... we lay down strips of Cork/tape and use as many self tapping sheet metal screws to secure the unit to the frame. I did some in 1979. and the unit is still there, the frame needs a little TLC in the paint dept. but still secure.
Most installations, have the units about the height yours is, but some customers want them as low as possible.
Sofar, I've only had two units transmit vibration into the house. One was because of a compressor problem, the other was on a wood foundation. We initially installed the unit on wall brackets because they wanted A/C before they landscaped the yard (common here). So when they complained of the vibes... I just moved the unit onto a sidewalk block, and we even got to keep the brackets for the next job.
Oh, and on that job, I got bit by a big black spider too!