In the latest game version, the Nericon's Garden gate is lockpickable (level 4 or 5 required IIRC).
Most re-release versions of the game should already be updated to the latest 1.0034A version, as shown in the bottom right corner of the main menu, so would not need to be
patched. The DVD version is already updated, and the patch (designed for the CD version) should not be installed.
There is also a second graveyard / Nericon's Garden key in the back room of the Ars Magicana alchemist; see
here and
here (Lockpick level 3 required).
If you don't have Lockpick (you can get 2 levels in the thieves' guild in Verdistis), you can give yourself the skill points to learn it with
iZakaroN's SaveEditor (or from
Kiya's site, with description).
Alternately, you can get a replacement key using the procedure in the
Lost Items topic, or can
hex teleport either into the garden or to the back of the alchemist's shop to get the key.
Welcome to the forum.

BTW, if you edit your duplicate post in the other forum, there is a 'Delete Post' button beside the 'Change Post' and preview buttons, which will remove the topic, as well (as long as nobody replies to it). This will not drop your post count.