So, without further ado, here are the 5 degrees of accessibility I came up with to describe this aspect:
- Passive Sharers: Willing to share spells (maybe for a price) but neither hoards nor actively seeks to share the knowledge.
- Active Sharers: Generally part of a guild or order, these people make their spells available to others. I further break Active Sharers down into Open Active Sharers (OAS) and Closed Active Sharers (CAS). OAS make their material available to anybody who wants access and may even advertise their material. CAS only make their materials available to members (possibly with even further restrictions) or impose other (financial?) restrictions.
- Regulated Sharing: Under this method the government of the city/state/nation/etc. restricts access to magical materials in one or more ways. This category is also broken down into two sub-categories: "Open" Regulated Sharing (ORS) and Closed Regulated Sharing (CRS). In ORS the government requires casters to register themselves and/or their spell research and may require that any sharing that is done be only with equally permitted members of society. Under the CRS system there is even heavier governmental involvement and in addition to the restrictions of the ORS system those seeking registration or permits must meet certain requirements or possibly even government (military?) rank.
- Hoarded: Wizards do not share their knowledge. They may fear/guard against theft or they may be driven by selfishness, power lust or a concern for the damage the knowledge could do in the wrong hands.
- Outlawed: This final category can actually be combined with a few of the above mentioned options. Under this category the city/state/national/etc. government makes the study/use/trade of magic illegal. It is either the sole realm of government use or not tolerated at all at any level. Casters must either hide or declare themselves and be hunted down. Foreign casters entering the country may either be hunted down as well or simply tracked and discouraged from attempting to settle down depending on the feelings of the region. Or they could be denied entrance outright.