Every town has a music store, and most have at least a few ukuleles, but maybe not a baritone. In Canada, the music store in many towns is Long & McQuade, and they were the source of my first baritone.

However, if you’re looking for something more distinctive, or of higher quality, you may have to search one of the ukulele-specific stores.

Long & McQuade
Stores from Newfoundland to British Columbia
https://www.long-mcquade.com/departments/1781/Guitars/Ukuleles/Baritone_Ukuleles.htm

Haliukes in Haliburton, ON
Fabulous collection of lovely, more unique instruments
https://haliukes.square.site/s/order?location=J9MCCGDAQ6RF7

Southern Ukulele Store, England
When I couldn’t find a Flight Fireball anywhere else, they had it and shipped from England
https://www.southernukulelestore.co.uk/shop-by-size/baritone/

Uke Like the Pros, California
Another uke-specific store that ships all over the world.
https://terrycartermusicstore.com/collections/ukulele-baritone

Sweetwater, USA
Amazing service and attention
https://www.sweetwater.com/c1053–Baritone_Ukuleles?_queryID=09a3c0839b45944c6bcc7be3f47c2971&_index=production_products

Reverb
An on-line marketplace of new and used instruments from all over the world. You never know what you might find.
https://reverb.com/marketplace?query=baritone%20ukulele&product_type=folk-instruments&category=ukuleles

Strings by Mail
Every type of string for any instrument, with great support team. 
https://www.stringsbymail.com

Direct from Manufacturer
Many manufacturers will ship direct, like Kala