Go to Everlook in winterspring and set yourself at war with them. Then kill the engineering supplies trainer and wait for him to respawn. When he respawns he'll have the schematic on him!
P.S. The guards WILL pwn you eventually so dont bother running that far. If your Friendly with them like I am then you only lose 25 rep. Respawn time is less than 5 mins.
Enjoy!
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OK, So I did this last night..and sure enough, worked like a charm. Although the respawn time felt more like 10 minutes. But I'm very excited to see what other vendor recipes I can get doing this..example, Argent Dawn !