You can do this with a relatively simple PowerShell script using the IPAM API in the newer versions (not sure what the version cutoff is for minimum requirements off-hand). There's a PS Cmdlet for querying the first available IP in a subnet, so all you'd have to do is build a connection to your SW server and give it a username/password then run that command.
More info on the IPAM API specifically: IPAM API · solarwinds/OrionSDK Wiki · GitHub
More info on the SDK (Installation, basic queries and scripts, docs): Home · solarwinds/OrionSDK Wiki · GitHub
Hope that helps!
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