If you go to this site, you can locate a Decathlon in Portugal, near where you will land.
Make sure it is a full-service store and not just a city store. The shops located in a city center typically are small shops. They will likely not have hiking poles.
You can view the store on the web site to get an idea. The stores located just outside a city center will be huge, and are usually reached by bus, metro or taxi. That is where you will find literally everything you could need to do a Camino.
Encontra todas as nossas lojas Decathlon
Use an online translator to translate Portuguese web pages as needed.
Decathlon is a sports SUPER STORE. It is typically huge, and has entire aisles dedicated to a single sport. It surpasses anything we have here in the US. They offer products that provide good value for the price paid. Their logos and house-brands will be the ones you see the most of on the Camino.
Hiking poles will not be a problem. Buy what you need. I have seen individual, adjustable aluminum poles that are more than suitable, for less than €10 each. In fact, one of the most seen hiking poles are the adjustable, turquoise-colored aluminum poles that usually sell for €6.99 or less each.
When I am volunteering at the Pilgrim Office, these are the poles most often abandoned at the end of a Camino. That is how I gauge their popularity. It seems that many pilgrims do not mind treating these poles as expendable at the end of their trip, especially if they want to avoid the hassle of trying to bring them home on an airplane, without checking them.
Hope this helps.
Tom