Hi Tim, the law changed which meant a spare wheel was no longer mandatory, so naturally manufacturers stopped supplying one as standard. A space saver spare wheel could be specified from new, but quite a lot of first time owners missed ticking that box and consequently, later owners question why there is no spare.
As Jim says above, these space savers can be sourced from the internet, but you need to know exactly what you are sourcing before committing to spend money. The Portfolio is likely fitted with 20-inch wheels, with different section front and rear, and large front callipers and accordingly a space saver is the option. Don't try and use an OEM front wheel on the rear hub as catastrophe lies in that direction.
The correct space saver can be obtained from companies like Road Hero, who sell via Kwik Fit. You would need the 19-inch space saver option to work with the Portfolio specification - to fit over the front calliper. The Road Hero comes as a kit, because you would also not have a jack, wheel brace, or chocks and all of these are included in the kit.
Hope this helps.
N6 JMX