Where can I buy Hollow Pipe?

As an alternative, look for Albion Alloys micro brass tube. Sprue Bros has them listed here: http://store.spruebrothers.com/category_s/2053.htm 

They're out of stock of the 0.3mm(OD)/0.1mm(ID) at the moment though.

I use hypodermic needles purchased by the box from Ebay. You can get them in any size and they're pretty inexpensive. Search on the internet for a chart which gives you the od and id of every size so you can telescope them if required. they come with a plastic insert attached to them which can easily be burned off with a match.

Micromark sells a bundle of assorted size brass tube: Here

And aluminum tube: Here

Flex-i-file also carries Albion Alloys - located in Canada, but their prices are USD.

https://www.flex-i-file.com/albion-alloys/albion-alloys-metals.php

 

regards,

Jack