A quick update- I found a great case on Ebay from finchball. The original creators of the HC508 don’t yet have one available so I purchased this one. It fits perfectly and makes the HC508 look much nicer on the side of the A500.
The construction is good, with 4 screws on the bottom holding the two halves together. There is good solid tight fit for the CF card so it doesn’t feel loose while inserted. There is even a small slot on the top half of the case to observe the disk activity led. You do however need to look directly down to see the LEDs.