I did call Makita direct but the young man that I got connected to from customer service did not know what a bushing is or even a template guide is used for. But assured me he has been wood working for many years at the end of our conversation he even ask what does PC stand for!
Well, Nicolas, if you were to ask a lot of woodworking people over here in Europe what "PC" meant, you'd probably get the same response - Porter-Cable are relatively unknown here these days having last been imported officially in the late 1970s/early 1980s. Similarly the PC screw type guide bush is also very little known here because the Trend-type (actually the Elu MOF96/deWalt DW615 type) is pretty widespread, but Makita do refer to their guide bush as a "templet guide" in their own use manuals (items 27 and 74 in the illustrations at the front of their own manual) so I don't understand why he didn't get that. But then again they refer to the clip-on frames used on belt sanders as "sanding shoes".....
Manufacturere do have a tendency to try to lock you in to their products, though, and guide bushes are a case in point. If you want to use P-C bushings why not just get yourself a piece of phenolic, acrylic or polycarbonate and just make your own? If you don't relish that then surely there must be a firm in the USA who make replacement base plates, e.g. Oak Park
? Sorry, I'm not in the USA, so some things are sort of "blind-side" for me, but even if a plate were too big there's no reason why it can't be fitted then trimmed to size using the motor with a bearing guided trim bit in another base (making sure that you hogged off the majority of the waste with a jigsaw or the like first). I'd also consider using the bought-in base as a master for other home-made sub-bases as well because all the holes are in the right places and are the right sizes. We have Trend over here (also in the USA) who do a "fits all" replacement sub base called a Unibase, which seem to fit almost every router on the planet, but they are really designed for bigger tools and would be too big for the RT0700 unless you want to hack a lot off round the edges after you've fitted it IMHO