Local nurseries usually do not grow their own crop of roses, but instead purchase the roses from a wholesale nursery. And I can guess they place their orders the year before for what they can sell during the height of the growing season. Hence why you will only see rose in a local nursery or garden center the spring and early summer before it gets to hot.

You will find the majority of smaller mail order nurseries such as Ashdown, Vintage, Roses Unlimited, Antique Rose Emorium, Chamblees, etc., propagate their own roses and on own root so they have a greater flexability of what they propagate and when, hence why they continue shipping during the year except for the hottest parts(usually mid June to mid Sept).

You local nursery you are talking to, is most likely getting ready to place their plant orders to their wholesalers for delivery for next year, hence why they told you Jan for the delivery date.

Hope this helps.

Here is a good article that explains the growing cycle for grafted roses (most are grown in Texas or in California in this country): The Tyler Rose Industry. There are only so many that are made available each year. Some are sold as bareroots (which are kept in cold storage and sold dormant early in the year), some are potted and sold wholesale to local nurseries as rosesnpots explained.

Own root vendors kinda have seasons too, some will have plants available year-round, others will stop shipping in the summer. It takes a lot less time to get a good root system on an own root rose, bur not all roses will do well on their own roots.