If you subscribe to the ISY portal, maybe to get echo integration, that also gives you IFTTT integration both inbound and outbound. From that you can build a limited SmartThings integration that may be all you need.
It’s also probable that you can use webcore instead of IFTTT just by using Webhooks, but you would need to check with the folks in the webcore forum on that.
In the past, people have used other “man in the middle” server options for communication with Insteon devices, but I have no idea which if any of those still work as they all look pretty old and some of the middleman devices are no longer made. But check with the folks in the following thread to see if they still have current integrations: