Hello, I’m looking for some real-world data which consist of at least one moving end-device with GPS data. And few at least 3-4 gateways hearing him. Is there something publicly available?
I want to try out some rough radio-localization in order to save up energy for an occasional GPS tracking. (I’m fine with +/- 1km accuracy so I hope it’s doable using gateway timestamps)
I’m afraid not 
If you want to try something yourself then perhaps look to Collos & TTN or other integrations 
http://preview.collos.org/
https://www.thethingsnetwork.org/docs/applications/collos/
https://www.loraserver.io/lora-geo-server/backends/semtech-collos/
An April 2018, 745 MB dump of TTN Mapper data is available at http://ttnmapper.org/dumps/ Quite a few of the mapping packets have been received by multiple gateways, like below. The timestamps in that dump won’t be good enough for your needs, but maybe SNR and RSI suffice:
id,time,nodeaddr,appeui,gwaddr,modulation,datarate,snr,rssi,freq,lat,lon,alt,accuracy,hdop,sats,provider,user_agent
...
4266913,2018-02-28 17:51:58,pycom-stuart,pytrack-mapper,B827EBFFFE2D3798,,SF7BW125,8.50,-96.00,868.300,50.936338,-1.396068,34.0,1.50,,,joris_binary,mqtt import v2
4266914,2018-02-28 17:51:58,pycom-stuart,pytrack-mapper,B827EBFFFEE36EF8,,SF7BW125,6.80,-96.00,868.300,50.936338,-1.396068,34.0,1.50,,,joris_binary,mqtt import v2
4266915,2018-02-28 17:51:58,pycom-stuart,pytrack-mapper,B827EBFFFEAC4B12,,SF7BW125,9.20,-101.00,868.300,50.936338,-1.396068,34.0,1.50,,,joris_binary,mqtt import v2
4266916,2018-02-28 17:51:58,pycom-stuart,pytrack-mapper,7276FFFFFE0103EC,,SF7BW125,-2.00,-117.00,868.300,50.936338,-1.396068,34.0,1.50,,,joris_binary,mqtt import v2
...
4266917,2018-02-28 17:52:09,pycom-stuart,pytrack-mapper,B827EBFFFEAC4B12,,SF7BW125,8.20,-103.00,868.300,50.936338,-1.395768,34.0,2.00,,,joris_binary,mqtt import v2
4266918,2018-02-28 17:52:09,pycom-stuart,pytrack-mapper,B827EBFFFE2D3798,,SF7BW125,7.80,-96.00,868.300,50.936338,-1.395768,34.0,2.00,,,joris_binary,mqtt import v2
4266919,2018-02-28 17:52:09,pycom-stuart,pytrack-mapper,B827EBFFFE71AB02,,SF7BW125,-5.00,-117.00,868.300,50.936338,-1.395768,34.0,2.00,,,joris_binary,mqtt import v2
4266920,2018-02-28 17:52:09,pycom-stuart,pytrack-mapper,7276FFFFFE0103EC,,SF7BW125,-10.00,0.00,868.300,50.936338,-1.395768,34.0,2.00,,,joris_binary,mqtt import v2
4266921,2018-02-28 17:52:09,pycom-stuart,pytrack-mapper,7276FFFFFE0103F0,,SF7BW125,13.00,-97.00,868.300,50.936338,-1.395768,34.0,2.00,,,joris_binary,mqtt import v2
...
4271737,2018-02-28 20:32:19,skydeck-adeunis-001,loramapping,000064517E807018,LORA,SF12BW125,-12.80,-123.00,868.100,52.521217,13.407333,0.0,,3.0,7,sats,ttn_http_integration_v2
4271738,2018-02-28 20:32:19,skydeck-adeunis-001,loramapping,7276FF000B030C96,LORA,SF12BW125,-10.00,-125.00,868.100,52.521217,13.407333,0.0,,3.0,7,sats,ttn_http_integration_v2
4271739,2018-02-28 20:32:19,skydeck-adeunis-001,loramapping,CAFFEEBABEDEADBE,LORA,SF12BW125,-3.80,-107.00,868.100,52.521217,13.407333,0.0,,3.0,7,sats,ttn_http_integration_v2
4271740,2018-02-28 20:32:19,skydeck-adeunis-001,loramapping,008000000000F3E4,LORA,SF12BW125,1.80,-97.00,868.100,52.521217,13.407333,0.0,,3.0,7,sats,ttn_http_integration_v2
4271741,2018-02-28 20:32:19,skydeck-adeunis-001,loramapping,0000024B08060246,LORA,SF12BW125,5.50,-82.00,868.100,52.521217,13.407333,0.0,,3.0,7,sats,ttn_http_integration_v2
Also, you’d need to get the gateway coordinates through some other means; see Determine which gateway is used by a given node. Beware that gateways might have moved since the packet was received.
See also http://ttnmapper.org/faq.php