Cable Modem Amplifiers?

A concerned Anonymous Coward asks: "Now that my cable modem system is filling up with users I cannot always get "online". The service provider's tech support says that my upstream signal power is borderline acceptable. They suggest that I buy a signal amplifier from them. I'm assuming they're trying to rip me off to offset capital investment costs. I've searched google for half and hour but cannot find anyone selling or anyplace to purchase a cable modem amplifier. Does anyone know where a cable modem amplifier can be purchased? Any advice on price, specs, quality, setup?" Cable modem amplifiers? I haven't heard of such things, but of course, that doesn't mean that they don't exist. Have any of you heard of such things, or is this just another attempt to separate the consumer from their money?