Not sure. As far as I know GFT isn't a tracker people just give away to anybody. Maybe make some useful posts, be active and helpful, and more importantly make some friends and you'll be more likely to get this invite gratis. I have GFT and I have over 30,000 Bonus points which is worth 3 invites if they we're available to purchase. Invites can only be purchased when donations are at 100%, which happens around the end of the month. But GFT doesn't always make it to 100% so actually getting invites to GFT is difficult because it has to be timed right.