Low B string available for the Rotosound Monet SM77 flatwound set(£38.99 on Amazon)  and .50 for the tapewounds ( £31.99 at Knighton Music Centre)   Flats: https://www.amazon.co.uk/Rotosound-Monel-Hybrid-Flatwound-Strings/dp/B0002GNY1Y/ref=sr_1_5?crid=2ZDUM7OWS4QL&keywords=Rotosound+Flatwound+Black+Steel+Strings+for+Electric+Bass+Guitar&qid=1678815801&s=musical-instruments&sprefix=rotosound+flatwound+black+steel+strings+for+electric+bass+guitar%2Cmi%2C116&sr=1-5