As a provider of MSDSs you are also a user. Economics dictates that you should first solve your own MSDS problem. It seems to have little relationship to the difficulty faced by your customer. Realize that the expense and frustration you experience in maintaining your own MSDS library, you are in turn creating for your customer. By taking the first step to break the chain and implement the solution of providing your documents in MSDS-Search, you can legitimately request that your vendors do the same.
All parties can then go to a single location to get the documents they require.
This is a good first step, but not the optimal solution. MSDSs are a standard reference document in both mission critical and non-critical situations. Access to them must be facilitated so they can be retrieved rapidly in an emergency situation. The number one request from users of MSDSs is that all documents be at a single location. The user simply does not know the name of the manufacturer.