Hello,
This is the 10" version of the filter that you previously had, so therefore it would not fit in your big blue cartridge.
The R30-20BB is still available, and we currently have them in stock. I have included the link to our webpage for that product for your convenience. Searching "155430-43" in the search bar will also get you to the product page as well.
If you any other questions or require assistance, please feel free to contact us and we will be happy to help.
https://www.wahlwater.com/Pentek-R30-20BB-Pleated-Sediment-Filter-155430-43_p_405.html