If I get this right you have:
- n "local PC's", let''s call them conventionally "TFTP Server B", "TFTP Server C", etc. to each of which a "group" of these Phones (let's call them Phone B1, B2 ... Bn, Phone C1, C2, Cn, etc.) are connected (LAN) and from which the phones download (periodically or on demand) some files.
- a "remote PC", let's call it "Central repository" where the actual files are hosted (and updated).
Traditionally in such a scenario, what is used is simply a (periodical, once a day, once every hour, etc.) synchronization of the local PC's to the Central repository, but what you have in mind is more like making a "bridge" between the TFTP request (initiated by the Phone(s) and directed to the local PC) and the WAN connection to the Central repository (where the download is served by an HTTP server, but it could be as well a ftp one or any other file transfer protocol).
So, basically, the Phone connects to the Local PC through TFTP and requests a file, if the file is missing on the Local PC a "normal" TFTP server will return an error "no such file", you want instead to have it try first downloading the "missing" file from the "Central Repository" and serve it.
Is this the idea?
If it is, there is something *similar* to this by the same Author of TFTP32:
but that is not suited for your situation, I believe.
What you need is more *like* the mechanism iPXE uses:
Cannot say if something *like* it exists (and if it exists for Windows).
Let's wait if some on the more "LAN oriented" members have some ideas.