There is not going to be any nice solution here. First the current VPNs will have all been built using a specific encryption domain. You can't just go and add in another office using a different subnet without having to rebuild all of those VPNs.
Your next problem - are you able to keep your current static IP address on your MX when you shift to your new office? Not all ISPs allow this. If you have to change that you'll be in a world of hurt having to rebuild everyone of those VPNs - and it wont be gradual - you'll have to do them all at the same time.
Considering only the scope of what has been given, I'd be using a couple of Cisco routers, like 890 series, 1100 series, and build a L2TPv3 connection between them - and extend the network at layer 2. Then you'll have exactly the same IP addressing.
You might be able to get a service provider to do this for you, but they'll usually want a fixed term contract.
I think you should consider the larger picture and resolve this at a grander [architecture] scale.
For example, for things what require an actual direct IP connection [not many these days] - we do all client management via Amazon AWS. We then connect our office into that. This means it doesn't matter what IP addressing our office has, or weather we are working remotely on client VPN.
However, very view things require an actual direct IP connection these days. There are a lot of remote access solutions that connect out and solve this problem. For example, Connectwise Automate.
For monitoring we use PRTG because you can put an agent on the client's premise and it connects out to report the monitoring data.
I encourage you to look at other solutions that don't require you to have a VPN.
