I Forgot to get the item at tears point,
That allows me summoning doomtrain.

Is there any known way of retrieving it in disc 3 / 4 ?

i dont think so on that one. it's not a drawn gf so you cant get it at ultimecia's castle. better pull out the gameshark and make yourself one of the item. otherwise you won't get him period. :\

You can "Draw" some of the gf's you missed from some boss, I cant remember which though

doomtrain can't be drawn. at the end of the game, the bosses you have to face to get your "functions" back you can withdraw from them if you get the draw function back from the first of them you face. then it's each one of the mini-bosses after that have a gf you can withdraw from them if you didn't have it already.

If u want all the gfs n saved over ur disc 3 file then i suggest remaking, i mean cmon its not that hard