A different tendon involved, but my Foot/ankle consultant is not doing PRP injections anymore - too many poor / bad outcomes. He takes things as far as ESWT and then surgery only if something odd comes out on the mri.
If you insist, go to a Dr and ask for private referral. Don't be surprised though if the treatment you seek is not offered. You may be left with a dent in the wallet and a cd full of mri images .
I'm of the school of thought that 26.2 miles is achievable for someone fit and healthy. Yes there will no doubt be some aches and pains during and after. The goal might be something like "just finish", the day might not be all plain sailing.
There is one glaring thing to address, and that is your marathon pace of 6km per hour. At this point in time you really don't know what your marathon pace is. If you based that on your half marathon time then you need to remember the caveat "provided you trained for the distance"
I think the message here is that there is no golden bullet. There is no single thing that will work for all. There isn't a guaranteed fix available from physios and medical practitioners.
the heel drop protocol is usually one of the first things recommended to me by other runners, physios, and surgeons. To give things a chance, stop running and follow the protocol religiously. We are not talking days here, we are talking weeks. Sometimes it worked out for me, other times it didn't. If it doesn't then there are plenty of other fixes available with varying odd of success.
I'm currently seeing an Orthopaedic Surgeon. He is adamant that using Alfredsons heel drop protocol combined with avoiding the aggravating cause is the first thing he would advise. It works for the majority, but doesn't always work out. My MRI scans of my Achilles show no healing taking place after 6 months having tries out most of the 1st line of attack approaches.
I'd tackle thinks head on and not put any pressure to do the 10k in Oct.