There seems to be some changes made in the asset packs recently, and they are moving more towards the SIMREADY assets. They were there a few months ago as I did download them. You can download the latest SIMREADY packs via the launcher under content tab
SIMREADY appears to be unrelated to Isaac Sim asset pack - they are different asset packages. Without the proper Isaac Sim asset pack structure, you’ll get errors like:
Isaac Sim Assets Pack have been removed. Please access assets through the “Isaac Assets (Beta)” tab in Window-> Browsers → Content, and there is no need to download them. internet is necessary to access it. For locally access assets, you may want to try downloading them first through the content brower: