I also looked around and could not find an 1/8" collet for the Enco manual mill (the manual mill takes standard R8 collets). You are already aware of the one McMaster-Carr has for $30.62 (claimed runout 0.0007"):
MSC Direct lists one, but it’s a genuine Hardinge (claimed runout 0.0005", $94.84, yikes!):
https://www.mscdirect.com/product/details/97821755
If you don’t object to ordering from Amazon, they have one for $7.75 + $6 (call it $14, claimed runout 0.0006"):
I hope this helps.
P.S. The fancy photo ads above happened automagically, I did all 3 as simple links.