Adobe does not sell Lightroom 5 anymore. Your only source would be to find it from a third-party seller such as Amazon or B & H Photo, etc. Here is the link where you can purchase Lightroom 6 from Adobe:
The button will prompt you to subscribe, but when you click on it you will be presented with the information to purchase. If this is an upgrade and you enter all of the information correctly, the price will change appropriately. Be aware that Lightroom 6 will not have some of the features that Lightroom CC has. Specifically, it will not have the dehaze filter and the panorama and HDR feature and some of the brush features. These were added after the release of Lightroom 6 and are not included in the Lightroom 6 license. When/if Lightroom 7 is released as a standalone upgrade these features will probably be added. But that will involve another upgrade purchase. It might be well for you to review the system requirements to ensure that your computer will handle Lightroom 6.
I think this is the direct link to buy LR6
-Lightroom serial number will work on both Windows and Mac versions https://forums.adobe.com/thread/2179765
Thanks, John. I seem to have lost that link. And the one I was using was automatically translating to English. Don't know what's going on with some of Adobe's websites lately.