I just mean make a new tx after each new block appears or at least at some regular interval so we can test building blocks knowing that one of these new tx types is included. Actually if there's an rpc call available to create one that would work as well... Then people testing can just create one when they need it.
I'm proposing one new RPC command: 'addmultisigaddress' ... that combines several public keys into one BIP 13 -style newfangled bitcoin address.
You get the public keys from the 'validateaddress' RPC command, which I've extended to give the full public key if you give it one of your bitcoin addresses.
I extended the 'send*' RPC commands so they know how to send to the newfangled bitcoin addresses, and can send coins you received as multisignature transactions if you hold all the corresponding private keys (listtransactions will also show you them, getbalance counts them in your balance, etc). So yes, anybody can generate new transactions to test...
Alan Reiner is proposing BIP 10 as the 'real' way to get multisignature transactions signed and spent: https://gist.github.com/1321518
(no implementation yet, as far as I know).