Why do you want an open public community that can be queried from any source IP? You don't have a network operations center with a well-known subnet?
See http://www.aerohive.com/330000/docs/help/english/6.2r1/hm/full/help.htm#config/com/ipAddrD.htm specifically the writeup on Wildcards. I haven't fully tested this myself (no SNMP querier handy), but I was successful at creating a wildcard address.
I managed to get it to work after using the type of configuration you mentioned above and the wildcards. Below is a screen shot of my config, we have three different IP Subnet Ranges in use throughout our district and by using this, it worked properly.
Many thanks for your assistance!