Hi Jacki, the Lynton range is very popular and items do sell out often. It isn't unusual for some pieces to be out of stock for extended periods. This problem is common where there are individual items in a collection that sell in far higher numbers than others.
There are still ongoing supply problems with products sourced from overseas I am afraid and Dunelm are not the only victim of this.
I should say that, in all honesty, there is no guarantee the 5-drawer unit will be re-stocked at all. I appreciate this isn't the response you wanted but it's a situation we've seen before and I would be doing you a disservice by not mentioning this.
I do hope this doesn't prove to be the case though.
Kind regards and sorry I wasn't able to help.