Suppliers

Straight Edges

H R Lamb and Son is located in the UK (and shipping worldwide). A selection his products can be found on this page.

For continuously cast iron bar, I find Wilmsetall to be a good source but it is hardly the only option. 

They can be found from  industrial suppliers in Europe, (in Germany they are called "Tuschierlineal" which will return more results than searching in English) 

Scraper blades and other supplies 

Surface Plates 

In Germany Johann Fischer and Planolith are both excellent (perhaps the best in the world) 

In southern Europe (France and Italy) Microplan is a good option

In the Netherlands Mytri  also offers very high quality products

Sweden Microbas

In the United States there is of course Starrett, but also other producers such as Standridge Granite.  Again going with a supplier close to home probably a good idea. 

Hardware and parts

In Europe 

Leadscrew stock: hfbshop.de/,  www.walzkraft.de/produkte/trapezgewindespindel, www.trapeziumdraad.nl/  

Ball Screws:  www.eichenberger.com/en/products/ball-screw 

Silver Solder: www.sonderlote.de 

Metal (steel, iron, bronze): wilmsmetall.de/