Allan & Borrows Island was being sold at Let's Sim which, unfortunately, shut down, so there's no way you can get the update there. But fear not: X-World Sceneries has you covered.
On a post at their official Facebook page, they explain what's coming and how to get the update:
Hey guys. Sorry for the lack of updates recently but as most of you probably already know I have been really busy with PropStrike making the Quatam River scenery.
About 3 weeks ago I got an email regarding the closure of Let's Sim. As you know I was selling my Allan & Borrows Island scenery exclusively on Let's Sim so this meant it would no longer be available for purchase. I started thinking of what to do with it and I finally decided to put a lot of the things I have learned since the release into an update which will improve the scenery and hopefully address the pet peeves I had with it when looking back. On top of that, I have decided to release this scenery on the upcoming PropStrike store. One of the reasons was I could fully control how I wanted to handle users who had already bought this scenery on the Let's Sim store. So, If you had bought the Allan & Burrows Island scenery on the Let's Sim store, write me an email where you just include the order number you will have received in the confirmation email. Then I will get back to you and put you on a list so as soon as the PropStrike store is up with the updated Allan & Burrows Island scenery you can pick it up and download it free of charge.
I hope that clears everything up and please if you have any questions let me know and I will do my best to answer them.
Here are a few screenshots of what I've been up to with the update. This is just the helipad/lighthouse part of it so there is more to come. Here's also a short video showing the now working lighthouse with an animated rotating light spill. https://youtu.be/6iaie8_eAe8
Email: [email protected]