We do not have any 802.11n VPN gateways. VPN endpoints are placed as business class products, and as such they suffer from the slower adoption of 802.11n in the business environment.
Unfortunately, I do not have any information I can release about upcoming VPN endpoint products.
I can't suggest products or solutions, but personally I would pursue distinct products for your wireless and vpn endpoint needs.
Also, if you are setting up a VPN to access your DNS-323 remotely it is worth noting that unless you have a NBNS server, NBNS name resolution will not happen over VPN and you will have to reference the DNS-323 by IP only.