Great questions. GMRS repeaters (sadly) don't all appear on some list. You have to do a lot of listening.
Thank GOD repeater input frequencies are not on bubble-packs (yet). That will ruin what is left of GMRS. Up until recently (thanks ebay), one needed a ICOM cheapie $125 at a minimum to get repeater capable, and that tends to keep most of the riff-raff out. If anyone buying a $10 set of radios from walmart could key up on a repeater they would all shut down pronto.
Even with these things in mind, most repeater users around here use some combination such as a ctcss code AND a dtmf code combined so that the moron jammers who DO go to the trouble of buying a duplex radio off ebay can't get it. It is frustrating because a legitimate user like myself who wants to pay to join the repeater group cant usually do it easily. The database isn't accurate for one thing, then on top of that even if you read their PL or DPL code, you don't know the other code they are using to lock people out, so you can't even talk to them, all because of the mess we have.
Why do we have it? The FCC allowed the sale of ultra-cheap radios to people without having to show a license, that are GMRS capable. Why one earth do $10 radios from the dollar store have GMRS output frequencies? Why? Why doesn't someone have to show a license to purchase GMRS equipment?
I have personally turned in companies for operating business on repeater outputs several times, and it is hard to get any action. The people running the Phoenix Cardinals stadium were using one of the frequencies for operations, and when notified they quit. A local garbage company still uses one and refuses to quit. The FCC seems powerless to stop them too, they just don't care really. For $30 now on ebay you can get a radio that WILL transmit on repeater input frequencies (though they are not duplex thank goodness), so the repeater owners have to work hard to protect their investment.
Sadly GMRS people haven't stood up for their service, and it is dying as a result. Hams are much more defensive of their bands, and will not tolerate illegal use, so they don't have as much of an issue.
GMRS is for licensed family use only.
FRS by the way is for FAMILY USE ONLY, not for department stores do operate "on the cheap" with (which many do). Not for parking lot attendants. These are ILLEGAL uses. But who enforces the law? Nobody. The FCC gladly takes GMRS license fees, but won't protect the service.
Bubble packs should be FRS only. The actual difference between 500 mw and 5 watts isn't much on flat terrain anyway (.75 mile vs. maybe 1.5 miles range at best). On top of this, with the horrible antennas on these little radios, the ERP is usually 2-3 watts max anyway. So that 5 watts is largely wasted, just eating batteries with minimal efficiency. You need a real commercial grade radio with a real antenna to get a good ERP from a UHF radio. I have seen ERP's of around 1 watt for a "5 watt" bubble-pack radio. Look at the type certification docs on some of these things.
It's a real shame the FCC allowed the creation of a cool service like GMRS, then charged too much for licensing, and provided no enforcement for the money. It has been all but ruined.
Some users migrate to ham licensing, but the whole purpose of GMRS is different than amatuer. One license covers my whole family, including my kids who have no business on amatuer radios. My wife isn't going to study for an amatuer license either. Everyone if your family would need one to accomplish what GMRS can do with one license, and for those without much money, they can use cheap radios for the whole family. Try that with amatuer equipment.
It's a shame, but we probably have three repeaters in our area and they are locked down tight.