Would it be possible to block 824-896 MHz all at once?

How would I go about doing this?

Isn't 824-896mhz the frequency for cell phones?

Now would I be able to block this frequency with relatively easy to find parts, and would I be able to block it over a 100' radius?

Of course it is possible to block (or more accurately jam) that freq range. Just set up a transmitter transmitting white noise or random junk at high power.

Some cell phones operate over that freq range, but not all.

It should be possible to build a jammer from available parts, but you'll be putting out a lot of interference over other parts of the radio spectrum. The radius of jamming would depend on transmission power.

Anywhere I could buy the parts offline to do this?

I figured it'd have to do with sending noise over the whole band, but I need a resource where I could figure out exactly how, like schematics or something.

I've googled it, but it only comes up with different forums of people asking how to do it.

Anywhere I could buy the parts offline to do this?

Probably the simplest jammer would be a modified spark-gap transmitter, with a bandpass filter to restrict most of the noise generated to the intended frequency range. As far as parts, I haven't actually designed the circuit for this (schematics/design aren't my specialty). I imagine you could get the basic parts from a normal electronics parts supplier.

You think it'd be worth building one, or would I be better off just buying one from say, phonejammers.com?

You got it all wrong, you gotta use your tin foil hat! Just messing with ya. If you have the skills, build it. If you aren't sure of yourself, buy it. Simple as that.