It's a strange problem, because I don't think it actually lets you request a lvl. 9 and under Legendary anymore. If you try to ask for something impossibru it doesn't accept it.
I've filled most of my dex via GTS and negotiations (sample of the last couple trades in the pic). Two ways you can do this:
#1: leave an exclusive or a hard-to-come-by poke (like Gliscor or something from the DW) and ask for something reasonable, or an exclusive-equivalent (mandibuzz for braviary). Give it a couple days and yer almost guaranteed it. When people come across something feasible to trade they jump at the opportunity. I got a Reshiram for a lvl.1 snorlax or something like that.
#2: Search Conditions: search for what you want (and it's evos and prevos too), starting at level nine and under in male, then check female, then increase in level and check each sex individually. When you search "all" you'll often only see a small portion of what may be a lot of opportunities, mostly cheated shinys from japan. Chances are, if the search conditions get you a full "spread" of possible trades, there may be more not shown. Even narrowing down the countries is sometimes necessary.
Or you know you could get Wifi general to spoon feed you.
