Unfortunately, the software is updated from year to year and there isn't really a way confirm whether it will be available online in the future.
Form 760C is available to print if you had mailed your tax return but as you stated, it is currently not supported for efiling. Please see this link for more information on what forms are supported for electronic filing for Virginia.
**Say "Thanks" by clicking the thumb icon in a post
**Mark the post that answers your question by clicking on "Mark as Best Answer"