Below are suggested email messages you can copy and edit/adapt to make it easy for you to invite the businesses you patronize to purchase a print ad in the commemorative festival program book.
Mix and match to create a compelling and friendly note.

Dear Sally,

[greeting, break the ice]
I hope you’re doing ok and you and your family’s health is good…

[transition]
I’m writing today on a different topic.

[Context]
I’m helping with the program book advertising  for the Max Reger Festival 150 – a weekend of concerts and lectures which will have a ~36-page commemorative program book available to all attendees. It will be professionally designed and printed, with a magazine-look and quality.
Max Reger was a phenomenal classical composer whose 150th birthday we are celebrating in Worcester.

[The Ask]
Would you consider an ad in our program?   Please see more information on these links.
Print Ad Overview/Prospectus(PDF)                Print Ad Price Sheet                Festival Information/Website
All ads also include a valuable web listing on our site, added to the ones already advertising.  As you can see this will include your logo, and all your social media and website links. Links on others’ websites are a good thing for search engine visibility!

Please let me know if you have any questions

Thank you for considering!   and I hope to see you soon …  for …

your closing