It's pretty easy to make your own add-on shelf out of a piece of aluminum 'U' channel, or to make a piece of 'U' channel out of two pieces of 'L' channel. I made one that way (out of 'L' channel that's about 1.5" on a side) using pop rivets, though epoxy would work as well. I just clip it to the music stand shelf with a couple of strong spring clips, and all my pens go in it, my glasses when necessary, and one of my tuners is always hung on it. It's also portable from one stand to another.
An alternative is to get a "cup holder" that clamps onto the upright tube of the stand -- like this one. It works well for glasses and a couple of pencils, etc.
Gary Merrill
Wessex EEb Bass tuba (DW 3XL or 2XL)
Mack Brass Compensating Euph (DE N106, Euph J, J9 euph)
Amati Oval Euph (DE 104, Euph J, J6 euph)
1924 Buescher 3-valve Eb tuba (with std US receiver), Kelly 25
Schiller American Heritage 7B clone bass trombone (DE LB K/K10/112/14 Lexan, Brass Ark MV50R)
1947 Olds "Standard" trombone (Olds #3)