I inherited a LAN that has a 192.0.0.x addressing scheme that is now running low on available IPs. We recently added about 70 Meru APs that just ate up my DHCP scope. What's the best way to subnet off of the 192.0.0.x network without having to change the whole address range? It would be such a pain to have to redo the whole network as there's so many proprietary IP devices that would have to be changed.

Thx

If you use routers with NAT, you could theoretically break this into 254 networks (.e.g. 192.168.0.1 -> WAN side of router -> NAT -> <rfc 1918 addr>.
The down side is that you won't be able to access every machine from every other machine, but only if they are within the same partition, or you have used PAT or NAT to make services available. Consequently, you will want to give some consideration to what and how you partition, but I would be surprised if there wasn't at least a group of several machines that don't need to accept inbound connections and hence could be partitioned off, freeing up that address.

If you have a switch that can do VLANs break off you AP's onto a subnet of their own.
Create a second DHCP Scope to service the devices on the VLAN. Then set your routing accordingly.

We broke each department off on their own VLAN, AP's are on a separate VLAN Servers are on another VLAN with ACL's

A lot of work but worth it.

It will take some reading, research and planning to set it up properly, and every network is different.

Old Network Adage Route once, switch many.

Not sure what you mean by 192.0.0.x

192.168.0.0/16 is a private subnet, is that the one you mean?

As a rule of thumb, you should plan your network to be broken up into chunks of about 200 devices, and assign each chunk their own subnet, VLAN, and DHCP scope if required.
A reasonable plan would be something like

192.168.1.0/24 -- WAN links (further broken down into /29 and /30 subnets for provider interconnection)
192.168.2.0/24 -- Servers
192.168.2.0/24 -- More Servers
192.168.3.0/24 -- VMotion VLAN/Virtualisation VLAN
192.168.254.0/24 -- Network Management
192.168.11.0/24 -- VLAN11 -- Building1, Floor1
192.168.12.0/24 -- VLAN12 -- Building1, Floor2 North
192.168.13.0/24 -- VLAN13 -- Building1, Floor2 South
192.168.14.0/24 -- VLAN14 -- Building2, Floor1
192.168.15.0/24 -- VLAN15 -- Building2, Floor2
etc....

Your DHCP server should have a scope for each of those VLANs.

You mentioned "proprietary IP devices" - do you mean devices with static IP addresses? If so, get them all reconfigured to use DHCP. There's nothing worse than having to rely on spreadsheets to manage your IP address assignments when the DHCP server can be doing it all for you.