The broker that will 'allow' scalping is the one that has the best STP (straight through processing) of trades. That is, there is no intervention between you the trader and the market maker - their software is taking care of the margining, etc. This means that they will have the fastest feed, the price that is closest to the market because they give the client direct access to the market. So it is probably the broker with the 'slow' feed and the classic 'bucketing' business model that will object to your trading patterns.

One of these brokers (out of 4 with the STP system) is Hotspot FXr, LLC in the U.S. I asked Barry E. Calder. SVP and one of the founders of the company, if they have had problems. He stated that of course, his company reserves the right to turn away a client, if the market maker complains that they are losing money because of a client's trading patterns. In practice, they would look for the evidence first and speak to the client, but according to Barry, it has never happened with them.

I suggest that you find such a company, but bear in mind that you will always have problems with the 'other' party if you are going to monitor 2 or more brokers to find the 'slow' feed. If you are just going to pick up on the very short term fluctuations in the market ('spikes' that are not wilfully generated by stop-hunting brokers), then I think any respectful broker with a serious market maker substantiating the prices would accept your business