Guild Wars 2

i am curious how you can get a small guild group for guild missions?
i am interested in doing it but most of my guild does pve, dungeons, wvw
curious also how u get a group for these with other guildies
not sure if this is the correct place to ask this

Quite often there are guilds hanging around in LA who will allow you to guest to there guild for Guild Missions (you might see an advert).

Or perhaps get your guild to start doing them at a pre organised time and invite people in temporarily from other guilds?