HD is a Makita dealer. Give them a P/N and they can order it.
If you can find the right person in the right mood. I used to be a Tool Rental tech (been out of the game for almost three years now), so I could order a good deal of parts through the rental system. I'd just mark them up to retail and sell them under a generic rental number, because I could get parts faster than through retail special order. I'm sure it probably violated company policy, but I cared more about getting results than following the book 100%.
I could not get everything Makita sells through rental (if it wasn't something in the rental fleet, I couldn't do it through the rental system), and when they come out with an updated part (new part number), I had to do a big dance of faxing forms to the home office and getting somebody there to activate the new part number, which could sometimes take over a month.
But if a customer who bought something new or used through the rental department needed parts, if I had it there, they would get it at a good price to get them back on the job fast. I sold a LOT of those Makita/Dolmar concrete saws...
There are ways to order more things through the retail system, but it can be "interesting" finding the right catalog and the right special order code and the right person at Makita to make it happen. It can be hit or miss. Tool rental, the tool corral, or the Pro Desk are the places to ask.
One of these days I'm going to actually score me a $200 6401 to play with, never did luck into one when I was working there.