How about making a template from Ply... then take this template and the pieces of stone and get them water jet cut...This process is very cheap to do..
I did a patch job last year and the customer had some provencale tiles down and no spares.. he traced the tile shape onto card and then got some tiles cut from a similar coloured 400 x400 tile and it cost about 20 quid for 4 cuts( tiles) to be done..
I got the 25 cut and rounded today,i used the wet saw then grinded the inner curve out to a respectable cut.I then used a rounding attachment in the grinder to put a quarter round on.Then used a flexible sanding disc to smooth all out before using finer grits to finish,worked well and i kept my helper busy too,got 20 fitted and a good bit of grouting done so tomorrow should finish all being well although the customer is taking me 14 mile away to look at a big house he wants me to do.pics will follow asap.
I learned on a 4" grinder couldnt get the shillings together for wet cutter when I started, its an extension of my arm now.
Of all the fandangled equipment and new ideas there are for cutting tiles of any size or shape the 4" is the one tool I still stand by.
If you can use one well then all else you need is your trowel and bucket especialy if your a stone fixer.
just completed 265 mtr referb of the old bank of england m/cr in jura limestone cut all radius cutting with my trusty 4 inch grinder then finished them with 120 & 220 disks