Below are places that sell tracts and booklets in the United Kingdom.
10 of Those
https://www.10ofthose.com/uk/special-offers/gospel-tracts
B McCall Barbour
Chick tracts
Chapter Two Books
https://www.chaptertwobooks.org.uk/tracts/gospel-tracts.html
https://www.chaptertwobooks.org.uk
Christian.co.uk
https://christian.co.uk/collections/tracts-and-booklets
Eden UK
Books, bibles tracts, music, children’s materials
Equipping the Church
http://www.equippingthechurch.com
Tracts and booklets
ICM Books Direct
https://www.icmbooksdirect.co.uk/category/1272/tracts
https://www.icmbooksdirect.co.uk
Living Waters Europe
https://shop.livingwaterseu.com/pages/gospel-tracts-uk
https://shop.livingwaterseu.com
SGM Lifewords
Tracts and booklets
The 4 Points
https://www.the4points.com/uk/christian_evangelism_tracts.php?cPath=8
The Good Book
https://www.thegoodbook.co.uk/outreach/evangelistic-booklets-and-tracts
Time for Truth
https://shop.timefortruth.co.uk/gospel-tracts-booklets.html
https://shop.timefortruth.co.uk
Trinitarian Bible Society - England
TBS sells low-priced Scripture tracts that give concise evangelical message. Each tract has an attractive natural color photograph cover design.