I get mine from Gryphon and have for 50 years. I make up my own sets, and the shop has a good variety of sizes. Most strings are manufactured by Mapes Wire; it means you can choose by availability and price. Essentially all the unwound ones are the same. Others will fill you in on ordering from internet dealers. .

I order straight from GHS

Strings & Beyond in NC

I used Strings by mail the last time.

I order directly from GHS website

I order HUBER true tone banjo strings from Banjo Ben.com.

I had to check to see if Dean Markley was still in business.
I haven't put them on yet, but i have them!

I now get all my strings from StringsByMail. Great company.

... at a music store  ... not any one in particular.  However, if there is a next time, I might try Amazon.

American Made Banjo Co.

http://Americanmadebanjo.com

I get mine from Roger Siminoff at Straight Up Strings.

https://straightupstrings.com/

In the UK - Newtone Strings. Make up your own sets

Another vote for AMB Cryogenics by mail from Florida. Not expensive. They will make up custom sets.

Strings by mail

i use those JD lights too. 

From GHS through their page on Amazon. Usually in 6 packs.

I buy a box of a dozen sets at a time from Elderly.

Banjo Ben and Sweetwater are the last two vendors I have ordered my banjo strings from.

Bobby

My last order was for wound third strings (0.018") from C.B. Gitty

https://www.cbgitty.com/guitar-instrument-parts/strings/bulk-12-packs-of-nickel-wound-electric-guitar-strings-choose-from-20-gauges/

https://www.cbgitty.com/guitar-instrument-parts/strings/bulk-12-packs-of-phosphor-bronze-wound-acoustic-guitar-strings-choose-from-20-gauges/

Bought my last strings (GHS PF190 - Americana Cryogenic light) from the previously mentioned Strings & Beyond. Four or six sets. I forget. Years ago, and two years in a row, I bought the same strings from Musician's Friend when their "Rocktober" sale included a good price on a 3-pack.

I have a very good acoustic instrument shop just a few blocks from home, but they don't stock the strings I like. Maybe I should ask them to carry them and I could buy a set every now and then to support them.

I've been waiting for Mapes Strings to put their banjo strings back on the site. The only thing they're currently selling other that piano wire is dulcimer sets. When banjo strings were on the site, they had two sets with a choice of 4th string windings, plus a build-your-own in gauges of your choice for $5 plus shipping.