The constructor for the TLM fifo has a size argument. The default size is ‘1’. But you can set it to whatever you want. A size of 0 implies no upper bound
Here is the portion of the source file.
// Function: new
//
// The ~name~ and ~parent~ are the normal uvm_component constructor arguments.
// The ~parent~ should be null if the <uvm_tlm_fifo> is going to be used in a
// statically elaborated construct (e.g., a module). The ~size~ indicates the
// maximum size of the FIFO; a value of zero indicates no upper bound.
function new(string name, uvm_component parent = null, int size = 1);