A month ago I would have been +1'ing this request.
But I've recently discovered the concept of the "Backup Server" in Alt.Binz, and since then have not had a single circumstance where I've run out of PAR2 files.
For example, I used Astraweb and they had an issue where lots of data from about 18 months to 6 months ago got corrupted. They weren't able to recover it. As such, even downloading something relatively new (such as in the time period of the previous posts) may not complete due to the damaged blocks outnumbering the available PAR2. Worse still, the PAR2 files are just as likely to have damaged blocks as the rar files.
A solution is to add (another) "block usenet account" as a Backup Server. This UseNet provider has to be a different provider to your primary UseNet provider. You can't just use another server or account from your Primary provider. By "block account" I mean a UseNet provider which lets you pay $x for yGB and those GB do not expire with time. For example, http://blocknews.net/
have a $4.50 for 10GB with no time period. I'm sure there are plenty of others.
Once you've configured a Backup Server, when Alt.Binz detects a damaged or missing block, it then automatically downloads that block from the backup server - no user interaction required.
In the past month I've been going back to download things which had previously failed due to excessive damaged/missing pieces. Thus far I've been able to get every single download. Some of the time, it hasn't even needed to use the PAR2 files!