The tracks in subway yards were somewhat farther apart than they were in railroad freight yards.
That's because of the third rail on each yard track that the subway cars would need.
Where a freight yard might have 2' or so between the sides of cars on adjacent tracks, a subway yard would have 3' or even more, in order to accomodate the third rails which are beyond the width of a subway carbody.
Run-around loops tenchically aren't needed as a subway train is bi-directional. However loops are used in certain areas. They are used to physically turn a train around in order to equalize wheel flange wear due to the curves in an assigned route.
Maintenance shops can be old early 20th century brick affairs/ They look something like the Atlas locomotive shop but longer. At least two such Atlas buildings joined together would make a decent looking older shop. Or, the more modern Butler Building type designs common to later 20th century construction. The MTA shop at Clifton on Staten Island would be an ideal one, easy to model.
Modern shops are not all that difficult to build from scratch, with suitable styrene siding, commercial window and door castings (Grandt Line). Specific kits for a subway maintenance shop probably don't exist. To build one, use and follow photos of a shop you'ld like to have.