A number of the distilleries have a members area you can join. Some will offer access to exclusive bottling and others will give you discounts and free whisky.

Here's the list of those I have found.
Kilchoman

Signing up to the Kilchoman Members area will provide you with discounts for clothing and certain bottles of whisky at the distillery, it also gives you access to bottling from the distillery which could be hard to find elsewhere.

go to the Kilchoman website https://kilchomandistillery.com and then click on Club Login at the top right hand corner of the page. From there you will see I want to create an account. Click on that and fill in your details.

Eventually they should send you a Pin Badge (which you should take with you to the distillery) and a Club Membership Card. They seem to send them out randomly, so don't expect them to turn up straight away.
Laphroaig

By joining Friends of Laphroaig you will be able to claim a lifetime lease on 1 square foot of land on Islay and claim a dram in ground rent per year. The dram can be collected on visiting the distillery.

To join the Friends of Laphroaig you will need to buy a bottle of Laphroaig Whisky which contains a code that you can use join. All details of how to claim you square foot of land and join Friends of Laphroaig are included in the bottles.