TWS have a section within the ‘Buy Wine’ area labelled ‘Wines for Laying Down’, which could be a place to look.
Lots of wines on the general pages have a drinking window of up to 5 years however, and depending on how much you like more mature wine with tertiary flavours I would say in general TWS give fairly conservative drinking windows and many wines will happily last longer than stated if stored well.
If you want to combine building a cellar with an element of discovery I can certainly recommend the Rising Stars vintage cellar plan at £28 per month. I’ve been signed up to this for the past 5-6 years and had some great wines I probably wouldn’t have otherwise tried. I’ll try draw up a list of what I’ve been allocated to give you an idea.
And finally, I’d suggest considering the En Primeur offers where some excellent wines can be found. Important to factor in your storage costs though when deciding what you feel is value for money.
Hope that helps a bit.
Most importantly, enjoy building, and then drinking your collection!