FR4 - eBay, Aliexpress, Taobao, plenty of sellers.
LPI - eBay, but you will also realistically need air compressor paint spray gun, and oven for pre-curing if you want "good quality". Even if you don't want "good quality" you are fighting an uphill battle to use this stuff on anything more than a few cm square. You are better to use dry film soldermask, this is not the same as dry film etch resist. Search Dynamask on eBay, it's about all you can get.
Silkscreen - Pulsar White TRF (Toner Reactive Foil) is probably the simplest, otherwise use white LPI with an actual silkscreen
Chemicals - Hydrochloric Acid (aka Muriatic Acid, Spirit of Salts) probably from your local hardware shop, Hydrogen Peroxide probably from your local pharmacy in Mexico, Sodium Carbonate/Percabonate for developing of dry film from your local grocery store (washing powder). More traditional etching products such as Ferric Chloride available on eBay delivered as dry powder I would expect.
Now to rain on the parade, etching your own PCBs is fine, good, do it all the time, but when you start looking to have soldermask and silkscreen, forget about it unless you want to do so on an industrial scale (become a PCB factory), just pay your $10 or 20 USD and have the boards made and shipped to you from China.