Home-made.
I visited our local hardwood emporium and had them cut the wood I selected to 2.75" square by whatever your desired length might be. I did not really care what wood, other than it was dimensionally stable (will not warp, etc.) as I plan to paint once my wife decides on a proper color.
The front-to-back pieces were all 'knotched' 2.75" x 2.75" at each end to 1/2 the 2.75" height. This securely "locks" the rack together when assembled.
The 1" threaded rod is from our local steel purveyor, along with 2.5" washers & nuts (need two washers & nuts per joint).
I drilled holes in the wood on 22" centers left-to-right and 19" centers front-to-back. This fits the granite sink cut-outs I purchased from our local granite counter-top supplier (cheap, as they are waste for them) and had them polish all sides - again, quite inexpensive as saves them the cost of disposing of a piece that is normally waste for them.
If I were to do again I would go with 24" centers on width and a 20" center front-to-back to provide a bit more 'freedom' in placing shelves and ease of use with a larger TT plinth.
The rack and shelves are very heavy at 400#+. Add to that the weight of the gear and it is going nowhere. Make sure you have the rack located where you want it before placing the shelves & gear on it. Very difficult to move once you have it fully loaded.
Works well of me in my basement listening area sitting on a poured concrete floor. Using a cell-phone app I've not been able to detect any vibrations/reflections in the audio range.
I used acoustic rubber under each corner of the granite shelves and the wood cut from a roll of I purchased from Ivan, but have forgotten the name. I do recall that Ivan said it was the last one he could get as they were no longer providing it in that format. If I were to do again I would purchase appropriate sized 'dots' from Herbie's to use under each corner of the shelves.
I would give some thought to stainless rod/nuts/washers if to do again. However, that would drive the price considerably. If memory serves I've got about $400 in the rack with the six granite shelves. I originally ordered the wood with enough length for an additional 3 shelves, but decided I only needed the six and cut the width accordingly.