How can I get my spawners to work when they are far away?

If you're up for modding, then I guess you're up for just editing the map!

You can adjust the Mob Spawner TileEntity Field for RequiredPlayerRange to something higher. This can be done with an MCEdit filter, there are a few of Texelelf's Filters that could do the job.

You really don't need any mods or any external program to do this! Do it straight from vanilla Minecraft via the /setblock command. Simply add the tag RequiredPlayerRange followed by the amount of blocks, and the command should look something like this:

/setblock (x) (y) (z) minecraft:mob_spawner 0 replace {RequiredPlayerRange:(blocks)} 

More info can be found watching Dragnoz's video here:

Hope this helps!