This: Ultimaker Bushing ID8*OD11*L22 is available in stock price at 0.7USD/pc. from RobotDig is the closest to the LM8UU size. The units you listed would work well in the Z axis pieces, and could be cut down for the rest. The problem is the OD is too snall on all of them. I hate remodding .stl's all the time, so I am looking at a different solution. We are playing with a sleeve that you can slide over each end of the bushing the 8x12x16 bushing and you would slide one of the printed parts over each end, amking the overall size of the unit the same as a LM8UU, so they would be able to be trapped in printed parts where there is already a spott for the exact LM8UU size. The bushing would be trapped inside the 2 printed parts, allowing it to fit anywhere a LM8UU would go. BTW, I am not sure if you know, but RobotDigg has an Alliexpress store where the prices are a little higher, but shipping is better, and often free. For instance, a 300x300mm heat pad is $20 on the website and crazy shipping, but it is $24 on the Alliexpress store with free shipping (sort of). Be carefull, because they will try to do an end run on you with quantity. I wanted to order 4 of the $24 heatpads that list free shipping, which they are as long as you order 2 or less. When you order 4, the shipping gets added back in and it is (you might want to guard your back side...) $132.00!!!!! If you can figure out the logic in this, you are better than me. I suggested that they divide the pas into packages of 2 (which they ship for free) and be on our merry way, but I guess it doesn't work that way in their world. The business guy in me wants to scream when I see things like this. If they would have been 2 dor $24 each, shipped, or 10 for $22 each, shipped, I would have bought 10, but their system punishes quantity orders. </RANT>
Oh yeah, I forgot, you could buy the 22mm long units and wrap them a couple of time with electrical tabe until the OD is where you want them, and be fine, but it is a little bit sketchy. They run VERY smooth. I am probably going to contact them for a bulk price on the 22mm long units, and see if there is a break to be had on the 30mm units for the Z axis units. In my builds, it would take 8 for the 30mm units to assemble the Z axis parts, and mine have 2 rods on each end.