No, unfortunately there are not, at least not for chlorine. Bromine tabs dissolve slowly even in hot water, but if you use those then your spa will become a bromine spa until you next change the water. That's not a terrible thing but may not be what you want. You would just continue to use chlorine though any spent bromine from the tabs (i.e. bromide ions) will become bromine again when you add chlorine. If you only use the tabs for a short time, then such bromine may go away over the following weeks as it slowly outgases and combines with organic bather waste so some may filter out -- it's a slow process, however, so if the bromine tabs are used for more than a few days then the resulting bromide may have the tub be a bromine tub for many weeks.
If you have a special feeder that is designed for Trichlor in a hot tub (and that's rare -- Aquafinesse used to have one, I believe), then you probably won't build up too much CYA if you are only talking about one week or less since the hot tub daily loss with no ozonator may only be 25% of the FC so perhaps 0.25 to 0.5 ppm FC per day. So even with a 4 ppm FC loss over the week, that's only around 2 ppm CYA. Fortunately, hot tubs don't use much chlorine in between soaks when there is no ozonator and when you let the water cool off (say to 80ºF or so).