I have not seen sinensis for sale in years, probably due to lack of demand. Calloways has a lot of Monrovia camellias when winter approaches but they are mostly japonicas with a few sasanquas. You may want to inquire if they will special order for you if there is still time to do that. Of the stores that I frequent, Calloways has/had (my opinion) the largest inventory of camellias but last year was so-so. So also check North Haven Gardens in Dallas off 75 and Archie's Gardenland in Fort Worth off Camp Bowie Blvd; their inventory numbers in the past were "ok" compared to Calloways. NHG will special order for you. I have never asked about special ordering at Archie's but I like their selection because they surprise with unusual camellias sometimes (instead of not just your usual Kramer's, Kanjiros, etc).

Oddly, the big stored HD and Lowes will once in a blue moon have interesting specimens too so they are woirth a check just to see what each year brings.

If ordering sinensis, you may want to order more than one shrub so as to have an adequate supply of leaves, especially if you drink a lot of tea.

Did you ever find your camellia sinensis?

Cameliashop.com is selling sinensis in a 4 plants pack (small plants, about 6-10" tall).

Here is a link that might be useful: Special prices at Camelliashop.com