I have found classical guitar strings which can be bought individually as well as by set via this website: stringsbymail.com. While I haven’t yet needed to order new strings the site offers nylon La Bella strings with guages .028, .032, .040, .029 wound, and you could buy another single .028 string for the 5th to match the 1st string. Seems pretty close to what Brian includes in his kits. BTW, I agree that tuning down to E tuning sounds just right on my gourd banjo.