While it is true that the teams routinely sell team bikes, riders generally have the option to purchase or are outright entitled to keep one or more of their bicycles. The specifics are normally delineated in the rider's contract.
I find that it is not at all unusual for a rider to have a few bikes from their career. Some have only one where others have 25+. It all goes to the individuality of each rider. It is fairly common for a rider who is not contractually entitled to the gift of one or more bikes to be at least offered the bike at a price lower than the team would otherwise sell to the general public. This often amounts to less than 2,500 euro for one of the cutting edge carbon wonders of today.
If you roll the clock back 25 or 30 years, riders rarely used more than 2-3 bikes for the entire season. There were notable exceptions like Eddy Merckx who rolled through bikes at a pace not seen again until recent times with Mario Cipollini. However, as a general rule, mere mortals survived back then on a couple of bikes. At the end of the season the bikes were pretty hammered.
Go back to pre-WWII and riders made do with even less. By the time you get to pre-WWI it was not uncommon that the pro riders bike was used either by himself or a combination of riders over two or more seasons.
I find if I want a specific rider's bicycle that I will contact that rider directly and try to arrange a deal before the season even begins. If I don't know the rider personally, I initiate contact via someone who does know the rider personally. That usually does the trick. If that approach does not pan out, I then go to the director of the team. The director route normally works without fail. Cash on the barrel head is a great motivator. I normally arrange to take possession of the bike at the end of the rider's season, preferably at the race where I can see with my own eyes the rider pedaling the bike across the finishing line.
I am very reluctant to obtain anything from sponsors unless they themselves are really cycling savvy. Even then, if it is a bike or jersey, I first route the legitimacy of the deal back through the rider and obtain a letter from the rider. The reason for this is that sponsors are often given replicas, particularly when it comes to jerseys.
When it comes to obtaining bikes from the family of a deceased rider, particularly one who rode more than 25 years ago, it is fairly easy to establish the validity of the bike. Since the riders back then generally had only a limited number of bikes to ride during a given season, I can normally find photographs of the rider on the exact bike. The way this is done is to mathematically measure angles from the photos, examine precise decal placement and components, then compare it all with the bike being offered for sale. No positive match, no sale.
Brett Horton San Francisco, CA
<snip> Isn't it the case that team bikes rarely stay in possession of the riders after a season is over or the rider moves on to another team? This has been the practice for years and years, from what I've read. If true, this would make your goals of obtaining a bike direct from a rider and/or family quite difficult, not to mention establishing the provenance of a bike once it has left the team and gone back to a manufacturer and/or sponsor. Dave Patrick <snip>
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