"Ordinarily" there are topographic maps available for any mapping GPS receiver. These may be proprietary maps available only through the manufacturer, or open-format maps available from third-party sources. I'm a long-time Garmin user and I know that Garmin's approach is the former. I know that Garmin doesn't sell any topographic maps of Turkey for their models. I'd be extremely surprised if any other major manufacturer does. The only online source of free map data that I'm familiar with (
GPSFileDepot) doesn't even list Turkey as one of the countries that you can search by.
As far as I can see, you have a few avenues you might want to explore:
There might be an off chance that some
little-known GPS brand that's active in the Turkish market but little known to readers of this forum could have topographic maps of Turkey available for their models. You can figure out what those brands are by looking through newspaper or magazine ads (or window shopping through electronics stores) in Turkey and seeing what brands are for sale. It should then be fairly easy to find the website of each manufacturer to check if they make any such topographic maps available.
Some GPS receiver models allow you to use
"custom maps". These consist of an image file essentially. You define (using appropriate software, as per the instructions of each manufacturer) the latitude and longtitude of two or three (or more) points on the map, and this allows the GPS receiver to deduce the orientation, position, and scale of the image and start showing it to you as a map. You can refer to this link for a detailed description and a list of Garmin models that have this feature (other brands do this, too):
Garmin Custom Maps
Of course, once you have this capability, the question you'll be faced with is
where to get the map imagery to use for custom maps. Due to the nature of these types of maps, you'll typically be limited to a small area (big enough for one ride perhaps) and a single zoom level, unfortunately. So, you could get by just taking screenshots of the "satellite" view of
Google Maps, or even its regular "map" view, for that matter.
Another source of topographic map imagery of Turkey for use as a custom GPS map could be this site that came up on the first page of the search results when I looked for "topographic map turkey" on Google:
Mapstor.com
Of course, they're not free. I don't know if you'll be willing to pay for maps on which you'll still have to spend effort to get into a GPS receiver.
OpenStreetMap might be another source of maps you can use for this purpose. This is the equivalent of an "open source" (or Wikipedia-like) project in the mapping world. Their maps show decent detail in Turkey. Even better, there is an
OpenCycleMap that's part of this project, too. That has good detail in Turkey as well, plus, it shows a topographic background. And, as I was browsing some areas near Istanbul just before writing this, believe it or not, I did see some stuff that looked like actual dirt trails represented on that map!
You could take screenshots of views of the OSM maps and use them as custom maps on a GPS receiver, or, if you want to get more sophisticated, you might want to try your hand at converting them into a format that your GPS could load directly. You may find your starting point for that kind of a personal project at this address:
OSM Map On Garmin
(While that page is Garmin-specific, I'm sure there must be information reachable through there that applies to other brands, too.)
When it comes to figuring out the latitude-longitude of a set of points on a map image in order to be able to use it as a custom map, if you are not aware of any tools that will allow you to do that,
Google Earth is one free program that can do that for you.
I hope this gives you at least some leads to pursue...
Thanks for the extensive explanation. Custom mapping is a good feature; although requires some workaround this may be used to apply what I want, but this is not available in Edge models 
