hiya guys, I'm having trouble with finding enough Missile Launchers, actually, I need 6 of them

So far I know the only ways to get missile Lauchers are to get the:
http://uk.games-workshop.com/storefr...0007&orignav=9
that's the Legion of the Damned Missile Laucher.
or the:
http://uk.games-workshop.com/storefr...1025&orignav=9
Tactical Squad Upgrade Sprue
and lastly one of the Chaos Havoc Models.
I really need those Missiles Launchers, what sort of sprue/bit could I get for this purpose without spending loads of money?
I know more people have this problem, and I hope that some of you can help us (the whole Space Marine players group) to get our Missiles out and ready.
Thanks in forward,
~Labora et ne Oleit
Wulfbanes