Just A work around way, do you have a Small Machine Shop in your town ?
If you so,do you have metal scrap yard in your town ? >
Go to the scrap yard and pickup some brass stock and stop by the machine shop with the brass and the router base plate and show them what you want to end up with.
It's small and quick job to do with the right equipment
(mill and a lathe)
The hard part for most small machine shops is getting the brass stock to do the job they run into min. buys on most of the stock they order and if your real luckey then may have some brass on hand but that's a long shot.
But once you do the running around it's duck soup to make the insert and rework the base plate a bit so they work as one.
Just a note *** if you have it done have them punch out the base plate hole to 3 3/4" so you use the new bigger panel bits and make a set of brass inserts to fit your new base plate setup. (1/2" i.d.,1" i.d.,1 3/4" I,D., 2 3/4" I.D. )Plus a 1 3/16" or 1 1/4" I.D. insert to hold the the brass guides.
P.C. type or Oak-Park brass guides.
Good Luck on your quest