Using .Net Core `AsSingleton<>` as a memory data provider?

I need to get a list of stations(lazily) from a remote service and to store it in DB and in memory.
Then, if someone wants the list, he tries to read the in memory list.
If it's null , it goes to Db and if there's no data in DB , it should go to a remote service , fetch the list , and to store the list in DB and in memory.

(Basically, I don't want to go to the remote service every request)

So I've used the .net core's singleton service :

services.AddSingleton<IStations,Stations>()

Where the class will contain the list itself :

public class Stations:IStations
{
 public List<StationModel> LstStationModel
        {
            get
            {
                lock (locker)
                {
                    if (_lstStationModel == null)

                    {
                        var ls = GetStationsFromDb().Result;
                        if (ls!=null && ls.Count > 0)
                            _lstStationModel = ls;
                        else
                            _lstStationModel = GetStationsFromProvider().Result;

                    }
                    return _lstStationModel;
                }
            }
            set
            {
                lock (locker)
                {
                    _lstStationModel = value;
                }
            }
        }
}

So now I have a single property in a singleton class .
When someone asks for the list , I check if it's null , then I go to db. If the db doesn't have the data , I start fetching from remote and fill the list.

I've also added lock , so that 2 requests won't invoke fetching twice.

Question

Something here doesn't look right. I was forced to use .Result rather than async await. I wantd to do it with property to have get and set. But I'm not sure it's the right way of dong it. And besides , I really don't like this solution.

Is there any way to do it in a more elegant/better way ?