I found two, via Google. More listed. Try these:
http://www.tvallowance.com/
The TV Allowance is a device that connects between a television and its supply of electricity. The TV Allowance controls the amount of time the television is allowed to be turned on. The TVA is a great tool for parents because it is a ‘set it and forget it’ device for them.
· Set blackout times to prevent usage during certain time.
· Set a weekly TV Allowance for up to six children.
· Each child is given a personalized 4-digit code that is entered to access the TV.
· The parental admin code is used in setup and to use the TV without deducting anyone’s allowance.
· The TV Allowance may also be used to control computer time by plugging in the computer monitor.
As children use up time watching TV, their account is debited. When the TV is shut off, the unit stops deducting time from that child’s account. When all of the time is used up, the TV shuts off and will not turn back on until the beginning of the next week when the allowance is automatically restored.
Blackout times can be set to block TV usage during homework or past bedtime hours. A parental override code is available to allow the use of the TV without debiting anyone’s account. Unused time may be rolled over to the next week or eliminated.
TV Allowance works by controlling power to the TV or video game console. Plug the TV’s power cord into the bottom of the unit, install three AAA batteries and lock the cover. The battery backup prevents the unit from being reset by unplugging the unit from the wall socket. The locked cover prevents tampering.
You can now follow the simple first time setup instructions to assign a four digit master PIN and a PIN for each child (important: let each child choose their own PIN), as well as inputting the number of hours per week allowed for each child.
http://www.akrontech.com/documents/enufftv.htm
Control when and how long your children will be in front of the TV!
Our children are glued to the screens 24/7 these days. Their weight is constantly on the rise as per recent statistics. Many of them are having social development problems because they don’t interact with other children as much. Their school work suffers in other cases. Their bed times are hard to enforce. They watch inappropriate shows on TV late at night. Recent studies also show that the average child in North America spends over 4 hours in front of a television every day. This is the average child and this is 4 hours a day in front of the TV! not to mention the time they spend using the computer. If we assume that our children come home from school around 3:00 pm and that they go to bed around 10:30 pm, this means that they are at home (awake) for about 6.5 hours each day (Mon-Fri).
Now lets take away 4 hours for TV viewing and even include some computer time (which was not part of the study!). This leaves only 2.5 hours per day which is usually spent having dinner, talking on the phone, doing other activities or …more screen! Not much time left for homework, physical activities or interacting with the family. There is no need to mention what happens during the weekends, is there? Control when and how long your children will be in front of the TV with ENUFF TV!