Hello Dan,
Unfortunately, GarageBand is not available for Windows, that's proprietary to Apple and their iOS and macOS devices. For what it's worth, you can endeavor on using virtualization like VMware (paid) or VirtualBox (free) but I doubt the legality of it, so tread carefully and do some research.
If you have an iPhone on hand, GarageBand on there is also free. Hopefully even the mobile version may be attuned to your specific needs, sometimes it comes with the phone or you have to install it from the App Store.
If you have a question about anything I've said here, please let me know and I'll be more than happy to clear anything up or help you further. Good luck.