I would like to create a large amount of local port forward ports to
another host. When setting them up on 1 putty session I get an error
at about the 42nd tunnel port that I have too many.

This is before I even try to connect to the server.

Due to new policies I need to set up tunnel sessions through 1 gateway
to up to 312 different ip/ports on the other side. NOT at one time
though. I want my users to be able to ssh 1 time to the gateway and
use a Procomm Directory to telnet to a max of 25 sessions at one time.
But these 25 sessions could be any combination of the 312 available
sessions.

Is there any way to increase the available local port fwd sessions on
one Putty session? Can you point me to any documentation to allow me
to increase this limit? Is there another alternative?

Example use
SSH from windows to UNIX gateway

On windows computer telnet to localhost 13000 - 13499 individually up
to 25 consecutive. Putty sets tunnel L13000=192.x.x.001:23 -
L13499=10.x.x.250:23 each local port being a separate server that can
only be accessed from the unix gateway.