Since I work in Law Enforcement ...
... my first thought is that you should probably contact the local Police. I see that you're in BC, so I don't know specifically what your laws say about theft, but most such laws are something along the lines of taking something with the "intent" to deprive the person of said property. So, if this landlord came into your residence and took the Tarot collection and is refusing to return it, that pretty much shows intent. If the collection is worth a lot, the theft may be a felony ($1000 or more in Arizona).
Also, you mentioned that it was an "old landlord". I take it that he/she is no longer your landlord. This brings up the question of how/why they were in your residence? If they were in your apartment without your permission when they weren't your current landlord, it may really up the ante on the crime. In Arizona (and most states), illegally entering a residence with the intent of committing a theft is "burglary" which is a felony regardless of the value of what was taken. Again, the actual theft shows the intent.
There is also the likelihood that the Police may be able to recover the collection quite easily when they talk to this person. It is amazing how willing some people are to return items when they're faced with going to prison.
If, on the other hand, this person felt they had a right to this property (say because you owed some back rent or something), you may find that the laws might very well be against them anyway. Unless the property is abandoned, such as you leaving the collection behind when you moved out of an apartment, a landlord is generally not allowed to just come in and take valuables from you. If that is the case, the Police can still give you your options or talk to this person about getting your property back.
At the worst, if he were allowed to take your decks for some odd reason, you may have to take him to court to get them back. But from the information you've provided so far, it is unlikely that their actions were legal.
