i use a combination of a script i wrote that uses ES and the restrict plugin for sourcemod.

Code:
block load
{
ma_say res_awp 1.0.Beta by siosios/n00b Unlimited Loaded

}

block commands 
{ 
   // Stick everything you want done here - 
   sm_restrict awp 0
} 

block com 
{ 
   // Stick everything you want done here - 
   sm_restrict awp 2

}
block comma 
{ 
   // Stick everything you want done here - 
   sm_restrict awp 4

}  
block command 
{ 
   // Stick everything you want done here - 
   sm_restrict awp 40
} 

event round_start 
{

   es_xsetinfo empty_players 0 
   es_getplayercount empty_players 
   if (server_var(tv_enable) = 1) do 
   {
      es_xmath empty_players - 1 
   }
    if (server_var(empty_players) < 10) do 
   {
    if (server_var(empty_players) > 0) do 
   {
      es_xdoblock restrict_awps/commands
      sm_csay restricting AWP's till a total of 10 people show up
   }
}
   if (server_var(empty_players) < 19) do
   {
       if (server_var(empty_players) > 9) do
      {
      es_xdoblock restrict_awps/com
      sm_csay restricting AWP's to 2 per team till a total of 20 people show up 
      }
   }
   if (server_var(empty_players) < 30) do
   {
       if (server_var(empty_players) > 19) do
        {
         es_xdoblock restrict_awps/comma
      sm_csay restricting AWP's to 4 per team till a total of 30 people show up
   }
}
   if (server_var(empty_players) > 30) do
   {
         es_xdoblock restrict_awps/command
      sm_csay UNrestricting AWP's..... AWP till your hearts content
   }
}
with

42 "Weapon Restrictions" (2.2) by Liam

sio