I think the best way to grind for any of the rare weapons is bronze league. Cheaply one can take an ai3 deck and make a bronze league deck out of it. try:
Grabix
Shrieker Rush
pvp speedbow (fav, fast, can beat grabix and shrieker)
I tried getting a FG deck together, but it's a pain. If you want to look at the FG unuped decklist, and try and kill 1 each day.... or just build one of these decks. they all play 75% or better vs bronze. you get better cards from the spins in bronze than ai3. Everyone you play will have a rare or two in it so you get a better chance of them in the normal spins. Then when you kill the 6th guy in a row you get the special spin for rares.
In about...15 hrs of gameplay lously over a week and a half at ai3 i got:
2x eternity
discord
2x titan
7x owls eye
5x shards
2x vampire daggar
1x pulverizor
Miracle
8x the 'sorry no nymph for you here's 65g card... forget what it's called.
3x druids staf
4x arsnic
2x pharos
You wont hit six in a row off the bat every time. dont worry when you loose 5-1 or 4-1 or 3-1... it happens. but your getting better spins since you are playing decks that ppl throw all their good stuff in. Not as good as gold/platnum, but vs ai3 grinding it's fast and fun to aquire cards, wins, gold, rares.
then when you have some wealth, and watching the spins isn't exciting anymore, go for false gods.
In both decks i happen to have the key for, just sub unupped cards where upped ones are.
SpeedBow. Cheap uber fun, very fast, great to learn, awesome vs ai3, pvp, BRONZE LEAGUE.
Hover over cards for details, click for permalink
4sa 4sa 4sa 4sa 4vh 4vh 4vj 4vj 4vj 4vj 4vj 4vj 52o 55q 55q 590 590 590 590 590 5c1 5c1 5f6 5f6 5i7 5og 5og 61q 61q 7tb 8pm
or: -poision -vamp dagger +2 arsnics.
Growing into the deck is fast, lots of things can be subbed around with and it can still be pretty successfull.
Shrieker Rush... just sub in the unupped where upped are.
Hover over cards for details, click for permalink
58o 58o 58o 58o 58o 58o 58o 58o 58o 58o 58o 58o 58o 58o 58o 58o 58o 58o 58v 591 591 591 591 591 77g 77g 77g 77g 77g 77g 8ps
Grabix is all over the forums, dont have it. BUT play bronze league and you'll quickly win most of the cards for it, since it is very popular.