The last Sage 200 version on 4.5.2 was (I think) 2021r1 (20.0.43.0). You can reference these assemblies (with Specific Version false), which are still on the Sage 200 Developers Downloads page (https://my.sage.co.uk/UK/communities/developers/developer-centres/sage-200/sage-200-product-downloads.aspx)
But don't deploy them - use whatever version the client has installed, using the documented method (https://my.sage.co.uk/Sage200SDKDocs/html/DOC0704_Overview.html) to resolve them.
As Sage have kept the AssemblyVersion of the client assemblies at 19.0.0.0, your product will then work with more-or-less any version of Sage 200.
PS. How weird that we can't put hyperlinks in this editor!
