I don't know the in's and out's of how the orders are placed, but if you say that that is done via NHS Supply Site, it doesn't absolve the government from responsibility.
The government made promises that PPE would arrive on Sunday, it still hasn't arrived - the UK have sent a plane but it is waiting in Turkey.
The government have declined to participate in the EU procurement scheme for PPE. This is likely to be a politically driven decision, but the bottom line is that hospitals are very low on reserves of PPE and that is threatening the lives of front line health workers.
Meanwhile millions of pieces of PPE are being shipped from Britain to the EU, because UK companies are being ignored by the government.
The government has made political decisions, rightly or wrongly - and they are ultimately reponsible for front line key workers having adequate PPE. If NHS Supply Site isn't working, they need to sort it out. They should have took part in the EU procurement system and they should make it much easier for UK manufacturers to supply the NHS.