According to tomaxxi.com, his site should be back up by 1 September.
Many (but not all) of his scripts are available on the https://creative.adobe.com/addons website. Unfortunately for the OP, TomaxxiForms was not one of them.
That said, if a script that was once online is no longer there, it may be for good reason. It may
* have catastrophic side-effects that aren’t easy to see;
* be that the developer has decided to make it available commercially rather than freely available in the public domain;
* have issues working in the latest versions of the software (particularly with older scripts) and need to be rewritten.
* be obsolete and no longer required.
And on that last point, InDesign has been able to do interactive forms since CS6 (May 2012), so I think the script no longer serves a purpose. Though I have never used Tomaxxi Forms so don’t know what it did compared to the functions in InDesign as it stands right now… or the OP is using a version of InDesign prior to CS6