You can share your A-mount lenses with an autofocus A-mount Minolta 35mm film body, but not an MC/MD-mount manual focus one--that's a completely different mount, different registration distance, different bayonet/physical linkage. No electronic communication. While you could, theoretically adapt with a ring, you'd have issues with vignetting if your A-mount lenses are for 1.5x crop, not full frame, and the not-so-small detail of not having an aperture ring to set aperture (remember, no electronic communication between the lens and the body in MD/MC). So, you have no way to set the aperture on the lens.
These reasons are probably why you can't find an adapter. Adapting MD/MC to A-mount can work, because those lenses have aperture rings, and you're typically adapting a full frame lens to a crop body, so there's no vignetting.
You basically need a autofocus Minolta film body that was made in 1985 or later. Unfortunately, your X-300 was made in 1984. In 1985, the Minolta A-mount was introduced with the Maxxum 7000, so any of those subsequent film bodies should work just fine with your A-mount lenses. You just might have vignetting if the lenses are for APS-C, not full-frame.
See also: Can I use lens brand X on interchangeable lens camera brand Y?