Some sort of online streaming service?
Buy the Blu Rays when they become available?
Alternate PBS stations? At this point they will be several episodes into the season, but if you record and keep the later episodes, they will be available for you as soon as you manage to get ahold of the earlier episodes.
Perhaps a PBS station that isn't showing it now will show it later. Do you have some sort of TIVO type of device that you can program to scan for and record the show if it suddenly comes on late at night and you haven't noticed?