Won't the normal phone shops have them (possibly for free)?
If not, Digitec have them in stock in Basel; https://www.digitec.ch/en/s1/product...cessory-281797
Either order online and go collect it from their shop downstairs in Markthalle or just pop in and order it directly there, though it'll take a bit longer.
Edit: Sorry, I was wrong Basel doesn't have them in stock. But if you order online before 07.00 on Monday, they'll have it early Monday afternoon (just select pickup from Basel in delivery options). They'll send an SMS when it arrives for an extra 20rp.