There can be, and should be a set of volume for the Shape and Material guidelines for Ars Magica rather than the few hundred offered. Not that a few hundred is a poor effort, its great. I think we should encourage more and more.
As a start here are a few ideas.
|A looped chain||Ring||+2|
|Lodestone||grants as Magnet Rego||+2|
|Lodestone||sympathy with Lightning||+2|
|Torc||ennobled presence and authority||+4|
A fair question is how easy or hard it is to “find” new Shape and Material bonuses, and the fairest answer I can give is that it is entirely dependent on the group of players.
My preference would be to let bonuses which are in line with the typical examples which are also very strongly present in the lore of mythic europe be “discovered” and use in the same season as they are required. ie. You create the Talisman and grant the bonus as active in the same season of activity.
A counter-point to this is to require a degree of investigation and experimentation to the process, thereby the Magus researches and confirms the bonus in a season of activity. This will suit longer games where a season of activity is not such a terrible loss of productivity. If this is the method chosen then the Magus must experiment during the season of investigation, and must roll a result which is not a disaster. The actual activity should be related to the bonus, and can easily be a spell or item using the form.
e.g. The magus wishing to confirm Lodestone as a shape and material bonus enchants a lesser invested device via experimentation, and succeeds in their result (I’d guess the magus keeps the magnitude of the effect very low) and gains the item, plus the discovery. As long as the magus successfully creates the item they also gain the discovery. A disaster in this process wrecks the item, and would also wreck the effort of trying to gain the bonus.
This is akin to the Discovery and Breakthrough rules in some of the sourcebooks, so will be no great surprise, the key difference is that the effort is greatly reduced from those rules.