Source for Dremel Stones / Diamond Sharpening Bits?

I have been using the $10 Dremel chain saw sharpening guide / attachment for a quick touch-up after each tank on my new Echo w/ Oregon chain to keep it cutting like new. My only complaint is that the stones wear out quickly (Particularly after needing to do the 4-5 passes after touching dirt / removing a stump, etc.) The typical Dremel 2-pack of stones (#453, 5/32, 4.0mm, blue; or #455, 7/32, 5.6mm, pink are the two I need for my saws.) are $6, not bad, but I noticed Widget supply (http://www.widgetsupply.com/page/WS/CTGY/dremel-chain-saw - I might also try their diamond hand files.) offers 5/32 in quantity for more like $1 each. 7/32 bits are harder to find. Does anyone have any info on sources or comparison to diamond? I assume diamond costs more but lasts longer?

Jim K in PA said:

Those Lee Valley ones appear to have about half the material that the eBay ones have, but are about 50 cents cheaper.

I bought two packs of the eBay stones, and shipping was free.

Now all I need is a Dremel tool! LOL - Father's Day is coming.

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Well it's not that simple. If you have one dremel to dedicate to saw sharpening, (Because you need it every day when sawing...), you'll want another for your regular tool box. Then you'll want a 12 volt one for using in the woods. (In my case I also want a 6 volt one as my tractor is 6V...) ;-)