Unfortunately it's not that simple. Items have two different levels - an item level and a required level. For example, for Manald Heal the required level is 24, but the item level is 27. So basically you can't get it from Kadala below level 27. (We had a discussion about this on Reddit before the season and together with a lot of people we gambled tens of thousands of shards on various levels between 0 and 28, and you can't get MH below level 27).
Someone was nice enough to write a script and query'd every item from the game API to list both required and minimum levels:
But there's more: some items can be gambled below their item level - for example, you can gamble Gungdo Gear on a level 1 monk, Lut Socks on a level 1 barb, and so on. Initially we thought it was just a -7 level reduction, but it doesn't make sense for the case of Gungdo Gear (which are not even the lowest bracers since Cesar's Memento have both lower item level and required level). So there seems to be some special rule for some (not all) low-level gambling slots/items.
Be careful with info you find about this - basically all of this we found out a week ago. So basically any "low level gambling guide" that's older than July 19, 2017 might contain wrong information. We really had no idea and are just scratching the surface here.