It varies a little by company, but most seed companies make their new stock available starting around December. Some hold off until January.
Re: Seeds. Yep. At Jung’s, in the last few years, I was stocking The Seed Wall (the BANE of my existence!) before Christmas and the catalogs had an earlier and earlier deadline each year it seemed.
I always order as soon as I can look through and make my selections for the year once the seed catalogs arrive. I usually order the same things from year to year - tried and true varieties for my Zone 4/5 garden. This year I selected some new, but all Determinate, tomatoes to try. I’m pretty happy with what I chose this season and a few will be repeats.
As Ellendra pointed out in an earlier thread, it would be wise to order as soon as the companies make things available as the wild weather this past growing season might make some seed varieties unavailable to us.
Thank you. Good to know.