S.R.U GBB is known for their non-standard but very interesting accessories for GBB replicas, such as Bullpup conversion kits for the AK family of carbines or the SCAR.
The first interesting information of the announcement of the SRU Heavily Modified AK Kit, which will make a replica to resemble the carbine seen in the movie "Elysium":
The manufacturers site offers also conversion kits for the GBB carbines from the AR and HK416 family:
The conversion kit currently costs 100 USD. The foregrip itself can be bought for 30 USD.
The Glock Bullpup SMG conversion kits are also available, they consist of a WE replicas placed inside a Bullpup conversion:
They can be bough for 162-315 USD depending on the version.
SRU: GHK G5 and WE PMC conversions