Hello Mohammad,
please do not be disappointed to find out that it not easy to find a halfway decent 2nd hand touring bike. First of all it is very much a matter of luck and being in the right place at the right time. Bicycle shops here in Germany are very limited in stocking used bicycles due to high shop rent and some other obligations, e.g. a very demanding liability situation. A dealer selling a used bicycle has to accept high responsibility for the quality of the bike, technical flaws and even -up to a certain degree- hidden damages can be a cause for hefty fines and compensations.
Bicycle dealers sometimes give a refund for a used bike to help a potential buyer making up his mind to buy a brand new one, in this case his intention is not selling a used bike, it is more of an incentive for the undecided customer.
Looking at the topics of this forum one can get the impression, that there is a big lot of high quality bikes to be seen in the streets, but, to be honest, only a very small minority of cyclists is willing to invest a month's wage in a bicycle.
Rideable, used bicycles basically come from this tiny small group, the big majority of everyday bicycles are used more or less thoughtlessly until major wear and tear is beyond repair (often due to high labour cost of the bike workshops). Hardly anybody would like to spent money on something that was not of very good quality when it was brand new.
Touring bikers are a more conservative lot when it comes to their equipment, there is a tendency to keep their (very often costy) eqipment in good condition as long as possible. In more than 30 years of riding I never sold one of my bikes, but they got stolen or destroyed in accidents.
Racing and mountain bikes are more considered a fashionable item amoung their users. A change in model or colour makes their "toys" look oldfashioned way before their technical lifespan, so your chances are maybe better finding a 26" mountainbike to convert it into a loaded-touring bike.
All this might sound a bit superstitious and arrogant, look at it as my personal impression of
the situation here in Germany.
So far for the bad news!
What I suggest: look at the mail order companies! They very often offer good value for a very good price. Some links:
http://www.roseversand.de/output/controller.aspx?cid=155&detail=2&detail2=562http://www.canyon.com/mountainbikes/Another source (even for used bicycles) is Ebay, but I do not know, how viable this solution is for you. it certainly takes a lot of precaution to buy from private sales in an online auction.
Very helpful are the classified advertisments not only in bicycle magazines, but also in daily newspapers.
http://www.bike-magazin.de/bko/show.php3?id=41&nodeid=41&ps_lo=0http://212.227.38.137/web/aktiv-radfahren/That's it for now, it is getting late, in the morning I have to work in my carpentry shop.
I hope I did not discourage you too much.
Good luck!
Axel