Not sure without looking for rack and pinion style rack suppliers in your local area. I would identify the rack pitch and size and search for a generic rack that matches.
Regarding the HF (Sieg X2) mini mill and mini lathe gibs, the originals are terrible fit and finish. Ended up milling new ones on an angle plate out of brass. Ill never go back. FAR less friction and you can tighten them better. 10x better than hours of lapping ever did. I made mine full height/thicknesd as well unlike the originals. Pressing bearings into the gib screw tips or simply leave them loose in the screw bores sounds very intriguing! If you use steel gibs maybe press rounded brass inserts into the screws. Either way if you have the machine apart drill out and tap for larger screws if the problem isn't solved by captive bearings so you have a sane diameter to work with. Far easier to adjust them that way too. Just be careful and keep everything aligned. LMS has nylock screws as well. Invaluable for quick and easy adjustments as they don't require the lock nuts. Technically you can cut a slot in the thread of your screws one by one and shove some sort of delrin or nylon lock strip in to accomplish the same. Tempted to convert the screws on my RF35 equivalent the same way.
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