You can use Power Custom Fields PRO for huge data sets. Still, showing all the options, without being able to select them by name can be a torture. So, you can limit the value count and filter them by name selecting the ones which contain those characters.
In order to do this, you can use argv["query"] only if you set the Filtering Strategy (from Autocomplete settings) to Datasource.
Video
See the following example for the routine usage:
Script details
The video used the following script:
string [] issues = selectIssues("created < now()");
string [] res;
for (string iss in issues) {
if (contains(iss.summary, argv["query"])) {
res = addElementIfNotExist(res, iss);
}
}
return res;