My personal experience with heat toner transfer method of making PCB. It works ONLY with laser printer.
Purpose of chemical tinning in last step is to protect copper against oxidation and provide good solderability.
Using Liquid tin is optional. Tinning can be done manually with regular solder, flux and iron.
All chemicals used in PCB manufacturing should be available at electronic hobby shop or can be found online.
There’s list of product distributors at manufacturer’s web site
My DIY tutorials and fun projects at