They are easier to find with marker lights.
Back in my Tau days...
http://www.thewarstore.com/product27332.html$10 for 6 missiles was the best deal I could find. As a bonus, I picked up a few of the turrets so I could use the devil fish as sky rays as needed (used magnets on the missiles)
Strangely enough, Battle Wagon Bits sells missiles for $2.50 each, so the 6 for $10 is the better deal.
I've yet to come across cheaper seeker missiles.
Cheaper missiles are easy enough to find from many sources, but if you want the boxy loaf of bread shaped missile, BWB seems to be the way to go.
-Matt
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