pfSense supports OpenVPN - you can use your own server/pc loaded up with the relevant number of NIC's. I've never used the OpenVPN functionality myself but everything else I've used I've found to be comprehesively featured and rock solid stable.
With a decent enough box, it possibly may handle your needs, although I believe bandwidth is more relevant to VPN throughput rather than number of tunnels.
Sorry I have only had a chance to test it with a 50Mb symmetric connnection and it wouldn't bottleneck at at all (as opposed to the previous router that claimed to support 90Mb of VPN throughput but only supported around 10Mb when I actually tested it!).
If this is of interest, set up a box you think may do the job, set it up and run the following command at a shell prompt and it will give a rough idea of expected VPN throughput.
openssl speed -evp aes-128-cbc