While MadeSolid’s website is down, their products are still being sold at major retailers and the website went down very recently (I was on it on Monday). I’m more inclined to believe that they’re switching hosts or upgrading the site than that they went out of business.
Regardless, I have worked with their Vorex Clear and Formlabs Clear, and have come to the conclusion that the yellowing is inevitable due to the material properties of the resin. Because they cure/harden at wavelengths similar to those emitted by the sun, any exposure to UV over time will inevitably cause yellowing. One way to delay this process is to coat the finished print with a UV protective sealant, and this will abate the yellowing for quite some time. If you really want a clear part, there is also other post-processing involved that will really improve the transparency of the part (see here and here). Obviously, these are pretty labor intensive processes.
The other alternative is to bypass SLA printers and find someone with a Stratasys Polyjet or 3DSystems printer who can print in VeroClear or similar. This is probably the closest you’ll get to true clarity/transparency but even then, it will yellow over time.